App passwords; CalDAV / CardDAV server for phones, Thunderbird, macOS

App passwords (SPEC App. D §D.5): one generated password per app, shown once,
revocable on its own, revoked on a password reset; never accepted by the web
sign-in. Settings → Security → App passwords (migration 0024).

CalDAV / CardDAV server (SPEC Appendix E), built in: /dav/ with
/.well-known/caldav|carddav, HTTP Basic with app passwords only (cached checks,
throttled failures). The calendar and contacts plugins serve their own tables as
collections (Plugin(dav=...)):
- calendars as iCalendar: series with overrides, time zones, all-day, attendees
  and RSVP, alarms <-> reminders; MKCALENDAR / PROPPATCH / DELETE of calendars;
  subscriptions read-only; writes to upstream-synced calendars flow on upstream;
- address books as vCard (3.0 served, 3.0/4.0 read), groups as CATEGORIES;
- what a client stores is served back verbatim until the web app edits it;
- sync tokens / CTags from change logs filled by triggers (calendar0008,
  contacts0002), so every write path counts; trimmed nightly after 90 days.
REPORTs: calendar-query (time range), calendar-/addressbook-multiget,
addressbook-query, sync-collection. nginx and the Vite proxy route /dav/.
Settings shows the server and user name to enter; install guide §5.4.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/api/__init__.py

@@ -49,6 +49,10 @@ def register_routers(app: FastAPI) -> None:
     ):
         app.include_router(router, prefix="/api")
     app.include_router(ws_router, prefix="/api")
+    # CalDAV / CardDAV (SPEC Appendix E): at the root, where clients look for it.
+    from app.dav.routes import router as dav_router
+
+    app.include_router(dav_router)
 
     # Mount discovered plugin routers at /api/plugins/{name} (SPEC §11). Hooks are
     # subscribed in the lifespan startup so they register once per process.

backend/app/dav/__init__.py

@@ -0,0 +1 @@
+"""CalDAV / CardDAV server (SPEC Appendix E)."""

backend/app/dav/auth.py

@@ -0,0 +1,93 @@
+"""Signing in a DAV client: HTTP Basic with an app password (SPEC App. E.2).
+
+Only app passwords: the account password (with or without 2FA) never works
+here, so a lost phone is one revocation away and 2FA cannot be bypassed. A
+sync makes many requests, each with the credentials; a successful check is
+remembered for a few minutes under a hash of the password, and forgotten as
+soon as the user's app passwords change (``app_passwords`` bumps a counter).
+"""
+
+from __future__ import annotations
+
+import base64
+import binascii
+import datetime as dt
+import hashlib
+import uuid
+
+from sqlalchemy import select, update
+
+from app.db import session_scope
+from app.identity import app_passwords
+from app.identity.service import resolve_handle
+from app.models import User, UserAppPassword
+from app.redis_client import get_redis
+
+CACHE_S = 300
+FAIL_WINDOW_S = 900
+MAX_FAILS_PER_ADDRESS = 10
+MAX_FAILS_PER_IP = 30
+_LAST_USED_EVERY = dt.timedelta(minutes=5)
+
+
+class Throttled(Exception):
+    """Too many failed sign-ins recently."""
+
+
+def _credentials(header: str | None) -> tuple[str, str] | None:
+    if not header or not header.lower().startswith("basic "):
+        return None
+    try:
+        decoded = base64.b64decode(header[6:].strip(), validate=True).decode("utf-8")
+    except (binascii.Error, UnicodeDecodeError):
+        return None
+    login, sep, password = decoded.partition(":")
+    return (login.strip(), password) if sep and login.strip() else None
+
+
+async def authenticate(header: str | None, ip: str) -> User | None:
+    """The user these Basic credentials sign in, or None. Raises Throttled."""
+    creds = _credentials(header)
+    if creds is None:
+        return None
+    login, password = creds
+    redis = get_redis()
+    handle = resolve_handle(login)
+    fail_keys = (f"dav:fail:addr:{handle}", f"dav:fail:ip:{ip}")
+    fails = [int(await redis.get(k) or 0) for k in fail_keys]
+    if fails[0] >= MAX_FAILS_PER_ADDRESS or fails[1] >= MAX_FAILS_PER_IP:
+        raise Throttled
+
+    async with session_scope() as db:
+        user = await db.scalar(select(User).where(User.handle == handle))
+        if user is None or user.blocked_at is not None:
+            await _failed(fail_keys)
+            return None
+        gen = int(await redis.get(app_passwords.generation_key(user.id)) or 0)
+        digest = hashlib.sha256(f"{user.id}:{password}".encode()).hexdigest()
+        cache_key = f"dav:auth:{user.id}:{gen}:{digest}"
+        if await redis.get(cache_key):
+            return user
+        row = await app_passwords.verify(db, user.id, password)
+        if row is None:
+            await _failed(fail_keys)
+            return None
+        await redis.set(cache_key, str(row.id), ex=CACHE_S)
+        now = dt.datetime.now(dt.UTC)
+        if row.last_used_at is None or now - row.last_used_at > _LAST_USED_EVERY:
+            await db.execute(
+                update(UserAppPassword).where(UserAppPassword.id == row.id).values(last_used_at=now)
+            )
+        db.expunge(user)
+        return user
+
+
+async def _failed(keys: tuple[str, ...]) -> None:
+    redis = get_redis()
+    for key in keys:
+        await redis.incr(key)
+        await redis.expire(key, FAIL_WINDOW_S)
+
+
+def user_id_of(user: User) -> uuid.UUID:
+    return user.id

backend/app/dav/provider.py

@@ -0,0 +1,118 @@
+"""What a plugin implements to serve its collections over DAV (SPEC App. E.1).
+
+The core (app/dav/routes.py) speaks the protocol; a provider only knows its
+own data: collections (calendars, address books) and the resources in them
+(one iCalendar object / one vCard each), named, with an ETag. Every method
+gets the signed-in user's id; providers open the user's RLS session
+(``sdk(name).session(user_id)``) themselves.
+"""
+
+from __future__ import annotations
+
+import uuid
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Literal, Protocol
+
+
+class DavError(Exception):
+    """A request the provider refuses: ``status`` is the HTTP answer
+    (403 read-only, 404 missing, 409 conflict, 412 precondition failed, 415
+    unsupported data); ``condition`` an optional DAV precondition element
+    (e.g. ``{urn:ietf:params:xml:ns:caldav}valid-calendar-data``)."""
+
+    def __init__(self, status: int, message: str = "", condition: str | None = None) -> None:
+        super().__init__(message or str(status))
+        self.status = status
+        self.condition = condition
+
+
+@dataclass
+class Collection:
+    id: str
+    displayname: str
+    sync_token: int  # the latest change number; also the CTag
+    description: str = ""
+    color: str | None = None  # "#rrggbb"
+    read_only: bool = False
+    components: list[str] = field(default_factory=lambda: ["VEVENT"])  # calendars only
+
+
+@dataclass
+class Resource:
+    name: str  # last path segment, e.g. "abc.ics"
+    etag: str  # without quotes
+    data: str | None = None  # the iCalendar / vCard text, when asked for
+
+
+@dataclass
+class Changes:
+    sync_token: int
+    changed: list[str]  # resource names changed or added since the old token
+    deleted: list[str]  # resource names gone since the old token
+
+
+class DavProvider(Protocol):
+    kind: Literal["calendar", "addressbook"]
+    content_type: str  # "text/calendar; charset=utf-8" / "text/vcard; charset=utf-8"
+    extension: str  # ".ics" / ".vcf"
+
+    async def collections(self, user_id: uuid.UUID) -> list[Collection]: ...
+
+    async def resources(self, user_id: uuid.UUID, collection_id: str) -> list[Resource]: ...
+
+    async def get(
+        self, user_id: uuid.UUID, collection_id: str, names: list[str] | None
+    ) -> list[Resource]: ...
+
+    async def put(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        name: str,
+        data: str,
+        *,
+        if_match: str | None,
+        if_none_match: bool,
+    ) -> tuple[str, bool]:
+        """Store ``data`` as ``name``; returns (new ETag, created)."""
+        ...
+
+    async def delete(
+        self, user_id: uuid.UUID, collection_id: str, name: str, *, if_match: str | None
+    ) -> None: ...
+
+    async def changes(self, user_id: uuid.UUID, collection_id: str, since: int) -> Changes | None:
+        """What changed after change number ``since``; None when that token is
+        too old to answer (the client then resyncs from scratch)."""
+        ...
+
+    async def create_collection(
+        self, user_id: uuid.UUID, collection_id: str, displayname: str, color: str | None
+    ) -> None:
+        """Create a collection at the id the client chose (MKCALENDAR / MKCOL);
+        DavError(403) when that id cannot be used."""
+        ...
+
+    async def update_collection(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        *,
+        displayname: str | None = None,
+        color: str | None = None,
+        description: str | None = None,
+    ) -> None: ...
+
+    async def delete_collection(self, user_id: uuid.UUID, collection_id: str) -> None: ...
+
+    async def query(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        start: datetime | None,
+        end: datetime | None,
+    ) -> list[str] | None:
+        """Calendars: names of resources with an occurrence overlapping the
+        range; None when the provider cannot filter (the core then returns all)."""
+        ...

backend/app/dav/routes.py

@@ -0,0 +1,595 @@
+"""The CalDAV / CardDAV endpoints (SPEC Appendix E).
+
+    /.well-known/caldav, /.well-known/carddav   → 301 /dav/
+    /dav/                                        root: points at the principal
+    /dav/principals/{user}/                      the signed-in user
+    /dav/calendars/{user}/[{calendar}/[{name}]]  calendar home, calendars, events
+    /dav/addressbooks/{user}/[{book}/[{name}]]   address-book home, books, contacts
+
+The data comes from the plugins' providers (app/dav/provider.py): the calendar
+plugin's for ``calendars``, the contacts plugin's for ``addressbooks``. Signed
+in with HTTP Basic and an app password only (app/dav/auth.py); session cookies
+are never looked at, so a web page cannot drive these endpoints.
+"""
+
+from __future__ import annotations
+
+import logging
+import uuid
+import xml.etree.ElementTree as ET
+from typing import Any
+from urllib.parse import quote, unquote, urlsplit
+
+from fastapi import APIRouter, Request, Response
+from fastapi.responses import RedirectResponse
+from sqlalchemy import select
+
+from app.dav import auth
+from app.dav.provider import Collection, DavError, DavProvider, Resource
+from app.dav.xml import (
+    CR,
+    CS,
+    A,
+    BadRequest,
+    C,
+    D,
+    Multistatus,
+    PropValue,
+    el,
+    error_body,
+    href,
+    mkcol_props,
+    parse,
+    propfind_request,
+    proppatch_request,
+    q,
+    report_request,
+)
+from app.db import session_scope
+from app.models import Account, User
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter()
+
+METHODS = [
+    "OPTIONS",
+    "PROPFIND",
+    "PROPPATCH",
+    "REPORT",
+    "GET",
+    "HEAD",
+    "PUT",
+    "DELETE",
+    "MKCALENDAR",
+    "MKCOL",
+]
+DAV_HEADER = "1, 3, calendar-access, addressbook, extended-mkcol"
+XML_TYPE = "application/xml; charset=utf-8"
+HOMES = {"calendars": "calendar", "addressbooks": "addressbook"}
+SYNC_PREFIX = "http://ultimo.email/ns/sync/"
+
+
+def _providers() -> dict[str, DavProvider]:
+    from app.plugins import loader
+
+    out: dict[str, DavProvider] = {}
+    for plugin in loader.get_plugins():
+        if plugin.dav is not None:
+            out[plugin.dav.kind] = plugin.dav
+    return out
+
+
+# ---- entry points ------------------------------------------------------------------
+
+
+@router.api_route("/.well-known/caldav", methods=["GET", "HEAD", "PROPFIND", "OPTIONS"])
+@router.api_route("/.well-known/carddav", methods=["GET", "HEAD", "PROPFIND", "OPTIONS"])
+async def well_known() -> Response:
+    return RedirectResponse("/dav/", status_code=301)
+
+
+@router.api_route("/dav", methods=METHODS)
+@router.api_route("/dav/{path:path}", methods=METHODS)
+async def dav(request: Request, path: str = "") -> Response:
+    method = request.method.upper()
+    if method == "OPTIONS":
+        return Response(
+            status_code=200,
+            headers={"DAV": DAV_HEADER, "Allow": ", ".join(METHODS), "Content-Length": "0"},
+        )
+    ip = request.client.host if request.client else ""
+    try:
+        user = await auth.authenticate(request.headers.get("authorization"), ip)
+    except auth.Throttled:
+        return Response(status_code=429, headers={"Retry-After": "900"})
+    if user is None:
+        return Response(
+            status_code=401,
+            headers={"WWW-Authenticate": 'Basic realm="Ultimo", charset="UTF-8"'},
+        )
+    parts = [unquote(p) for p in path.split("/") if p]
+    ctx = _Ctx(request, user, parts)
+    try:
+        return await ctx.handle(method)
+    except BadRequest as err:
+        return Response(status_code=400, content=str(err))
+    except DavError as err:
+        body = error_body(err.condition) if err.condition else b""
+        return Response(
+            status_code=err.status,
+            content=body,
+            media_type=XML_TYPE if body else None,
+        )
+
+
+class _Ctx:
+    def __init__(self, request: Request, user: User, parts: list[str]) -> None:
+        self.request = request
+        self.user = user
+        self.uid = str(user.id)
+        self.parts = parts
+        self.providers = _providers()
+
+    # -- paths -----------------------------------------------------------------------
+
+    def principal(self) -> str:
+        return f"/dav/principals/{self.uid}/"
+
+    def home(self, segment: str) -> str:
+        return f"/dav/{segment}/{self.uid}/"
+
+    def coll_href(self, segment: str, coll_id: str) -> str:
+        return f"{self.home(segment)}{quote(coll_id, safe='')}/"
+
+    def res_href(self, segment: str, coll_id: str, name: str) -> str:
+        return f"{self.coll_href(segment, coll_id)}{quote(name, safe='')}"
+
+    # -- dispatch --------------------------------------------------------------------
+
+    async def handle(self, method: str) -> Response:
+        p = self.parts
+        if not p:
+            return await self.root(method)
+        if p[0] == "principals":
+            if len(p) != 2 or p[1] != self.uid:
+                raise DavError(404)
+            return await self.principal_req(method)
+        if p[0] in HOMES and len(p) >= 2:
+            if p[1] != self.uid:
+                raise DavError(403)
+            provider = self.providers.get(HOMES[p[0]])
+            if provider is None:
+                raise DavError(404)
+            if len(p) == 2:
+                return await self.home_req(method, p[0], provider)
+            if len(p) == 3:
+                return await self.collection_req(method, p[0], provider, p[2])
+            if len(p) == 4:
+                return await self.resource_req(method, p[0], provider, p[2], p[3])
+        raise DavError(404)
+
+    async def body(self) -> ET.Element | None:
+        return parse(await self.request.body())
+
+    def depth(self) -> int:
+        value = (self.request.headers.get("depth") or "1").strip().lower()
+        return 0 if value == "0" else 1
+
+    @staticmethod
+    def multistatus(ms: Multistatus) -> Response:
+        return Response(status_code=207, content=ms.to_bytes(), media_type=XML_TYPE)
+
+    async def respond_props(
+        self, items: list[tuple[str, dict[str, PropValue]]], method_root: ET.Element | None
+    ) -> Response:
+        req = propfind_request(method_root)
+        ms = Multistatus()
+        for path, props in items:
+            if req.names_only:
+                ms.response(path, dict.fromkeys(props))
+            elif req.names is None:
+                ms.response(path, props)
+            else:
+                found = {n: props[n] for n in req.names if n in props}
+                missing = [n for n in req.names if n not in props]
+                ms.response(path, found, missing)
+        return self.multistatus(ms)
+
+    # -- root and principal ----------------------------------------------------------
+
+    def common(self) -> dict[str, PropValue]:
+        return {
+            q(D, "current-user-principal"): [href(self.principal())],
+            q(D, "principal-URL"): [href(self.principal())],
+            q(D, "owner"): [href(self.principal())],
+        }
+
+    async def root(self, method: str) -> Response:
+        if method != "PROPFIND":
+            return Response(status_code=200 if method in ("GET", "HEAD") else 405)
+        props = {**self.common(), q(D, "resourcetype"): [el(q(D, "collection"))]}
+        return await self.respond_props([("/dav/", props)], await self.body())
+
+    async def addresses(self) -> list[str]:
+        async with session_scope() as db:
+            emails = list(
+                await db.scalars(select(Account.email).where(Account.user_id == self.user.id))
+            )
+        out = [self.user.handle, *emails]
+        return list(dict.fromkeys(e.lower() for e in out))
+
+    async def principal_props(self) -> dict[str, PropValue]:
+        props = {
+            **self.common(),
+            q(D, "resourcetype"): [el(q(D, "principal")), el(q(D, "collection"))],
+            q(D, "displayname"): self.user.handle,
+            q(C, "calendar-user-address-set"): [
+                href(f"mailto:{a}") for a in await self.addresses()
+            ],
+            q(C, "calendar-user-type"): "INDIVIDUAL",
+            q(D, "principal-collection-set"): [href("/dav/principals/")],
+            q(D, "supported-report-set"): [],
+        }
+        if "calendar" in self.providers:
+            props[q(C, "calendar-home-set")] = [href(self.home("calendars"))]
+        if "addressbook" in self.providers:
+            props[q(CR, "addressbook-home-set")] = [href(self.home("addressbooks"))]
+        return props
+
+    async def principal_req(self, method: str) -> Response:
+        if method == "PROPFIND":
+            return await self.respond_props(
+                [(self.principal(), await self.principal_props())], await self.body()
+            )
+        if method == "REPORT":  # principal-property-search, expand-property: nothing to add
+            return self.multistatus(Multistatus())
+        return Response(status_code=405)
+
+    # -- homes -------------------------------------------------------------------------
+
+    def privileges(self, read_only: bool) -> list[ET.Element]:
+        names = ["read", "read-current-user-privilege-set"]
+        if not read_only:
+            names += ["write", "write-content", "write-properties", "bind", "unbind"]
+        return [el(q(D, "privilege"), children=[el(q(D, n))]) for n in names]
+
+    def reports(self, kind: str) -> list[ET.Element]:
+        ns, reports = (
+            (C, ["calendar-query", "calendar-multiget"])
+            if kind == "calendar"
+            else (CR, ["addressbook-query", "addressbook-multiget"])
+        )
+        items = [(ns, r) for r in reports] + [(D, "sync-collection")]
+        return [
+            el(q(D, "supported-report"), children=[el(q(D, "report"), children=[el(q(n, r))])])
+            for n, r in items
+        ]
+
+    async def home_req(self, method: str, segment: str, provider: DavProvider) -> Response:
+        if method == "PROPFIND":
+            home_props: dict[str, PropValue] = {
+                **self.common(),
+                q(D, "resourcetype"): [el(q(D, "collection"))],
+                q(D, "displayname"): "Calendars" if provider.kind == "calendar" else "Contacts",
+                q(D, "current-user-privilege-set"): self.privileges(False),
+            }
+            items = [(self.home(segment), home_props)]
+            if self.depth():
+                for coll in await provider.collections(self.user.id):
+                    items.append(
+                        (self.coll_href(segment, coll.id), self.collection_props(provider, coll))
+                    )
+            return await self.respond_props(items, await self.body())
+        if method == "REPORT":
+            return self.multistatus(Multistatus())
+        if method in ("GET", "HEAD"):
+            return Response(status_code=200)
+        return Response(status_code=405)
+
+    # -- collections -------------------------------------------------------------------
+
+    def collection_props(self, provider: DavProvider, coll: Collection) -> dict[str, PropValue]:
+        token = f"{SYNC_PREFIX}{coll.sync_token}"
+        props: dict[str, PropValue] = {
+            **self.common(),
+            q(D, "displayname"): coll.displayname,
+            q(D, "current-user-privilege-set"): self.privileges(coll.read_only),
+            q(D, "supported-report-set"): self.reports(provider.kind),
+            q(D, "sync-token"): token,
+            q(CS, "getctag"): str(coll.sync_token),
+        }
+        if provider.kind == "calendar":
+            props[q(D, "resourcetype")] = [el(q(D, "collection")), el(q(C, "calendar"))]
+            props[q(C, "supported-calendar-component-set")] = [
+                el(q(C, "comp"), attrs={"name": comp}) for comp in coll.components
+            ]
+            props[q(C, "supported-calendar-data")] = [
+                el(q(C, "calendar-data"), attrs={"content-type": "text/calendar", "version": "2.0"})
+            ]
+            props[q(C, "calendar-description")] = coll.description
+            if coll.color:
+                props[q(A, "calendar-color")] = coll.color
+        else:
+            props[q(D, "resourcetype")] = [el(q(D, "collection")), el(q(CR, "addressbook"))]
+            props[q(CR, "supported-address-data")] = [
+                el(
+                    q(CR, "address-data-type"),
+                    attrs={"content-type": "text/vcard", "version": "3.0"},
+                ),
+                el(
+                    q(CR, "address-data-type"),
+                    attrs={"content-type": "text/vcard", "version": "4.0"},
+                ),
+            ]
+            props[q(CR, "addressbook-description")] = coll.description
+        return props
+
+    async def find(self, provider: DavProvider, coll_id: str) -> Collection:
+        for coll in await provider.collections(self.user.id):
+            if coll.id == coll_id:
+                return coll
+        raise DavError(404)
+
+    def resource_props(
+        self, provider: DavProvider, res: Resource, with_data: bool
+    ) -> dict[str, PropValue]:
+        props: dict[str, PropValue] = {
+            q(D, "getetag"): f'"{res.etag}"',
+            q(D, "getcontenttype"): provider.content_type,
+            q(D, "resourcetype"): [],
+        }
+        if with_data and res.data is not None:
+            data_prop = (
+                q(C, "calendar-data") if provider.kind == "calendar" else q(CR, "address-data")
+            )
+            props[data_prop] = res.data
+        return props
+
+    async def collection_req(
+        self, method: str, segment: str, provider: DavProvider, coll_id: str
+    ) -> Response:
+        if method == "MKCALENDAR" or method == "MKCOL":
+            return await self.make_collection(segment, provider, coll_id)
+        coll = await self.find(provider, coll_id)
+        if method == "PROPFIND":
+            items = [(self.coll_href(segment, coll.id), self.collection_props(provider, coll))]
+            if self.depth():
+                for res in await provider.resources(self.user.id, coll.id):
+                    items.append(
+                        (
+                            self.res_href(segment, coll.id, res.name),
+                            self.resource_props(provider, res, False),
+                        )
+                    )
+            return await self.respond_props(items, await self.body())
+        if method == "REPORT":
+            return await self.report(segment, provider, coll)
+        if method == "PROPPATCH":
+            return await self.proppatch(segment, provider, coll)
+        if method == "DELETE":
+            if coll.read_only:
+                raise DavError(403)
+            await provider.delete_collection(self.user.id, coll.id)
+            return Response(status_code=204)
+        if method in ("GET", "HEAD"):
+            return Response(status_code=200)
+        return Response(status_code=405)
+
+    async def make_collection(self, segment: str, provider: DavProvider, coll_id: str) -> Response:
+        if any(c.id == coll_id for c in await provider.collections(self.user.id)):
+            raise DavError(405)  # exists already
+        root = await self.body()
+        props = mkcol_props(root)
+        rtype = props.get(q(D, "resourcetype"))
+        if self.request.method.upper() == "MKCOL" and (
+            rtype is None
+            or rtype.find(q(CR, "addressbook")) is None
+            or provider.kind != "addressbook"
+        ):
+            raise DavError(403)
+        if self.request.method.upper() == "MKCALENDAR" and provider.kind != "calendar":
+            raise DavError(403)
+        name_el = props.get(q(D, "displayname"))
+        color_el = props.get(q(A, "calendar-color"))
+        await provider.create_collection(
+            self.user.id,
+            coll_id,
+            (name_el.text or "").strip() if name_el is not None else "",
+            (color_el.text or "").strip() if color_el is not None else None,
+        )
+        return Response(status_code=201)
+
+    async def proppatch(self, segment: str, provider: DavProvider, coll: Collection) -> Response:
+        patch = proppatch_request(await self.body())
+        if coll.read_only:
+            raise DavError(403)
+        values: dict[str, Any] = {}
+        for name, value in patch.set.items():
+            text = (value.text or "").strip()
+            if name == q(D, "displayname"):
+                values["displayname"] = text
+            elif name == q(A, "calendar-color"):
+                values["color"] = text
+            elif name in (q(C, "calendar-description"), q(CR, "addressbook-description")):
+                values["description"] = text
+        if values:
+            await provider.update_collection(self.user.id, coll.id, **values)
+        # Properties not kept (calendar order, …) are accepted and ignored:
+        # clients treat a refusal as a failed sync.
+        ms = Multistatus()
+        ms.response(self.coll_href(segment, coll.id), dict.fromkeys([*patch.set, *patch.remove]))
+        return self.multistatus(ms)
+
+    async def report(self, segment: str, provider: DavProvider, coll: Collection) -> Response:
+        root = await self.body()
+        if root is None:
+            raise BadRequest("empty report")
+        rep = report_request(root)
+        wants_data = rep.props is None or any(
+            p in (q(C, "calendar-data"), q(CR, "address-data")) for p in rep.props
+        )
+        ms = Multistatus()
+
+        def add(res: Resource) -> None:
+            props = self.resource_props(provider, res, wants_data)
+            if rep.props is None:
+                ms.response(self.res_href(segment, coll.id, res.name), props)
+            else:
+                found = {n: props[n] for n in rep.props if n in props}
+                missing = [n for n in rep.props if n not in props]
+                ms.response(self.res_href(segment, coll.id, res.name), found, missing)
+
+        if rep.kind in ("calendar-multiget", "addressbook-multiget"):
+            names = [_last_segment(h) for h in rep.hrefs]
+            got = {r.name: r for r in await provider.get(self.user.id, coll.id, names)}
+            for h, name in zip(rep.hrefs, names, strict=True):
+                if name in got:
+                    add(got[name])
+                else:
+                    ms.response(h, {}, status=404)
+            return self.multistatus(ms)
+
+        if rep.kind in ("calendar-query", "addressbook-query"):
+            names_q = (
+                await provider.query(self.user.id, coll.id, rep.start, rep.end)
+                if rep.kind == "calendar-query"
+                else None
+            )
+            for res in (
+                await provider.get(self.user.id, coll.id, names_q)
+                if wants_data
+                else (
+                    await provider.resources(self.user.id, coll.id)
+                    if names_q is None
+                    else [
+                        r
+                        for r in await provider.resources(self.user.id, coll.id)
+                        if r.name in set(names_q)
+                    ]
+                )
+            ):
+                add(res)
+            return self.multistatus(ms)
+
+        # sync-collection (RFC 6578)
+        since = _token_number(rep.sync_token)
+        if rep.sync_token and since is None:
+            raise DavError(403, condition=q(D, "valid-sync-token"))
+        if since is None:
+            changed = None
+            deleted: list[str] = []
+            token = coll.sync_token
+        else:
+            changes = await provider.changes(self.user.id, coll.id, since)
+            if changes is None:
+                raise DavError(403, condition=q(D, "valid-sync-token"))
+            changed, deleted, token = changes.changed, changes.deleted, changes.sync_token
+        if changed is None:
+            resources = (
+                await provider.get(self.user.id, coll.id, None)
+                if wants_data
+                else await provider.resources(self.user.id, coll.id)
+            )
+        elif changed:
+            resources = (
+                await provider.get(self.user.id, coll.id, changed)
+                if wants_data
+                else [
+                    r
+                    for r in await provider.resources(self.user.id, coll.id)
+                    if r.name in set(changed)
+                ]
+            )
+        else:
+            resources = []
+        present = {r.name for r in resources}
+        for res in resources:
+            add(res)
+        for name in deleted:
+            if name not in present:
+                ms.response(self.res_href(segment, coll.id, name), {}, status=404)
+        ms.sync_token(f"{SYNC_PREFIX}{token}")
+        return self.multistatus(ms)
+
+    # -- resources ---------------------------------------------------------------------
+
+    async def resource_req(
+        self, method: str, segment: str, provider: DavProvider, coll_id: str, name: str
+    ) -> Response:
+        coll = await self.find(provider, coll_id)
+        if method in ("GET", "HEAD"):
+            got = await provider.get(self.user.id, coll.id, [name])
+            if not got:
+                raise DavError(404)
+            res = got[0]
+            content = (res.data or "").encode() if method == "GET" else b""
+            return Response(
+                status_code=200,
+                content=content,
+                media_type=provider.content_type,
+                headers={"ETag": f'"{res.etag}"'},
+            )
+        if method == "PROPFIND":
+            got = await provider.get(self.user.id, coll.id, [name])
+            if not got:
+                raise DavError(404)
+            return await self.respond_props(
+                [
+                    (
+                        self.res_href(segment, coll.id, name),
+                        self.resource_props(provider, got[0], True),
+                    )
+                ],
+                await self.body(),
+            )
+        if method == "PUT":
+            if coll.read_only:
+                raise DavError(403, condition=q(D, "need-privileges"))
+            data = (await self.request.body()).decode("utf-8", "replace")
+            etag, created = await provider.put(
+                self.user.id,
+                coll.id,
+                name,
+                data,
+                if_match=_etag_header(self.request.headers.get("if-match")),
+                if_none_match=(self.request.headers.get("if-none-match") or "").strip() == "*",
+            )
+            return Response(status_code=201 if created else 204, headers={"ETag": f'"{etag}"'})
+        if method == "DELETE":
+            if coll.read_only:
+                raise DavError(403)
+            await provider.delete(
+                self.user.id,
+                coll.id,
+                name,
+                if_match=_etag_header(self.request.headers.get("if-match")),
+            )
+            return Response(status_code=204)
+        return Response(status_code=405)
+
+
+def _last_segment(h: str) -> str:
+    path = urlsplit(h).path
+    return unquote(path.rstrip("/").rsplit("/", 1)[-1])
+
+
+def _token_number(token: str) -> int | None:
+    if not token:
+        return None
+    tail = token.rsplit("/", 1)[-1]
+    return int(tail) if tail.isdigit() else None
+
+
+def _etag_header(value: str | None) -> str | None:
+    if not value:
+        return None
+    value = value.strip()
+    if value == "*":
+        return "*"
+    if value.startswith("W/"):
+        value = value[2:]
+    return value.strip('"')
+
+
+__all__ = ["router", "uuid"]

backend/app/dav/xml.py

@@ -0,0 +1,236 @@
+"""WebDAV XML: reading request bodies, writing multistatus answers (RFC 4918,
+4791, 6352, 6578). Properties are ``{namespace}name`` strings, as ElementTree
+names them."""
+
+from __future__ import annotations
+
+import xml.etree.ElementTree as ET
+from dataclasses import dataclass, field
+from datetime import UTC, datetime
+
+from defusedxml import ElementTree as SafeET
+
+D = "DAV:"
+C = "urn:ietf:params:xml:ns:caldav"
+CR = "urn:ietf:params:xml:ns:carddav"
+CS = "http://calendarserver.org/ns/"
+A = "http://apple.com/ns/ical/"
+
+for _prefix, _ns in (("d", D), ("cal", C), ("card", CR), ("cs", CS), ("ical", A)):
+    ET.register_namespace(_prefix, _ns)
+
+
+def q(ns: str, name: str) -> str:
+    return f"{{{ns}}}{name}"
+
+
+class BadRequest(Exception):
+    pass
+
+
+def parse(body: bytes) -> ET.Element | None:
+    if not body.strip():
+        return None
+    try:
+        root = SafeET.fromstring(body)
+    except Exception as err:  # noqa: BLE001 - any malformed XML is the client's error
+        raise BadRequest(str(err)) from err
+    return root  # type: ignore[no-any-return]
+
+
+@dataclass
+class PropRequest:
+    """PROPFIND: which properties (None = all)."""
+
+    names: list[str] | None = None
+    names_only: bool = False
+
+
+def propfind_request(root: ET.Element | None) -> PropRequest:
+    if root is None or root.find(q(D, "allprop")) is not None:
+        return PropRequest()
+    if root.find(q(D, "propname")) is not None:
+        return PropRequest(names_only=True)
+    prop = root.find(q(D, "prop"))
+    if prop is None:
+        return PropRequest()
+    return PropRequest(names=[child.tag for child in prop])
+
+
+def requested_props(root: ET.Element) -> list[str] | None:
+    prop = root.find(q(D, "prop"))
+    if prop is None:
+        return None
+    return [child.tag for child in prop]
+
+
+@dataclass
+class Report:
+    # calendar-query | calendar-multiget | addressbook-query | addressbook-multiget
+    # | sync-collection
+    kind: str
+    props: list[str] | None
+    hrefs: list[str] = field(default_factory=list)
+    start: datetime | None = None
+    end: datetime | None = None
+    sync_token: str = ""
+    limit: int | None = None
+
+
+def _ical_time(value: str | None) -> datetime | None:
+    if not value:
+        return None
+    try:
+        return datetime.strptime(value.strip(), "%Y%m%dT%H%M%SZ").replace(tzinfo=UTC)
+    except ValueError:
+        return None
+
+
+def report_request(root: ET.Element) -> Report:
+    tag = root.tag
+    names = {
+        q(C, "calendar-query"): "calendar-query",
+        q(C, "calendar-multiget"): "calendar-multiget",
+        q(CR, "addressbook-query"): "addressbook-query",
+        q(CR, "addressbook-multiget"): "addressbook-multiget",
+        q(D, "sync-collection"): "sync-collection",
+    }
+    kind = names.get(tag)
+    if kind is None:
+        raise BadRequest(f"unsupported report {tag}")
+    rep = Report(kind=kind, props=requested_props(root))
+    rep.hrefs = [(h.text or "").strip() for h in root.findall(q(D, "href"))]
+    if kind == "calendar-query":
+        tr = root.find(f".//{q(C, 'time-range')}")
+        if tr is not None:
+            rep.start = _ical_time(tr.get("start"))
+            rep.end = _ical_time(tr.get("end"))
+    if kind == "sync-collection":
+        rep.sync_token = (root.findtext(q(D, "sync-token")) or "").strip()
+        nresults = root.find(f"{q(D, 'limit')}/{q(D, 'nresults')}")
+        if nresults is not None and (nresults.text or "").strip().isdigit():
+            rep.limit = int((nresults.text or "").strip())
+    return rep
+
+
+@dataclass
+class PropPatch:
+    set: dict[str, ET.Element] = field(default_factory=dict)
+    remove: list[str] = field(default_factory=list)
+
+
+def proppatch_request(root: ET.Element | None) -> PropPatch:
+    out = PropPatch()
+    if root is None:
+        return out
+    for action in root:
+        prop = action.find(q(D, "prop"))
+        if prop is None:
+            continue
+        for child in prop:
+            if action.tag == q(D, "set"):
+                out.set[child.tag] = child
+            elif action.tag == q(D, "remove"):
+                out.remove.append(child.tag)
+    return out
+
+
+def mkcol_props(root: ET.Element | None) -> dict[str, ET.Element]:
+    """MKCALENDAR / extended MKCOL: the properties to set on the new collection."""
+    if root is None:
+        return {}
+    out: dict[str, ET.Element] = {}
+    for sett in root.findall(q(D, "set")):
+        prop = sett.find(q(D, "prop"))
+        if prop is not None:
+            for child in prop:
+                out[child.tag] = child
+    return out
+
+
+# ---- answers --------------------------------------------------------------------------
+
+# A property's value: text, a list of child elements, or an element builder.
+PropValue = str | list[ET.Element] | None
+
+
+class Multistatus:
+    def __init__(self) -> None:
+        self.root = ET.Element(q(D, "multistatus"))
+
+    def response(
+        self,
+        href: str,
+        found: dict[str, PropValue],
+        missing: list[str] | None = None,
+        status: int | None = None,
+    ) -> None:
+        resp = ET.SubElement(self.root, q(D, "response"))
+        ET.SubElement(resp, q(D, "href")).text = href
+        if status is not None:
+            ET.SubElement(resp, q(D, "status")).text = _status_line(status)
+            return
+        if found:
+            ps = ET.SubElement(resp, q(D, "propstat"))
+            prop = ET.SubElement(ps, q(D, "prop"))
+            for name, value in found.items():
+                el = ET.SubElement(prop, name)
+                if isinstance(value, str):
+                    el.text = value
+                elif isinstance(value, list):
+                    el.extend(value)
+            ET.SubElement(ps, q(D, "status")).text = _status_line(200)
+        if missing:
+            ps = ET.SubElement(resp, q(D, "propstat"))
+            prop = ET.SubElement(ps, q(D, "prop"))
+            for name in missing:
+                ET.SubElement(prop, name)
+            ET.SubElement(ps, q(D, "status")).text = _status_line(404)
+
+    def sync_token(self, token: str) -> None:
+        ET.SubElement(self.root, q(D, "sync-token")).text = token
+
+    def to_bytes(self) -> bytes:
+        body: bytes = ET.tostring(self.root, encoding="utf-8")
+        return b'<?xml version="1.0" encoding="utf-8"?>\n' + body
+
+
+def el(
+    tag: str,
+    text: str | None = None,
+    children: list[ET.Element] | None = None,
+    attrs: dict[str, str] | None = None,
+) -> ET.Element:
+    e = ET.Element(tag, attrs or {})
+    if text is not None:
+        e.text = text
+    if children:
+        e.extend(children)
+    return e
+
+
+def href(path: str) -> ET.Element:
+    return el(q(D, "href"), path)
+
+
+def error_body(condition: str) -> bytes:
+    root = ET.Element(q(D, "error"))
+    ET.SubElement(root, condition)
+    return b'<?xml version="1.0" encoding="utf-8"?>\n' + bytes(ET.tostring(root, encoding="utf-8"))
+
+
+_REASONS = {
+    200: "OK",
+    201: "Created",
+    204: "No Content",
+    207: "Multi-Status",
+    403: "Forbidden",
+    404: "Not Found",
+    409: "Conflict",
+    412: "Precondition Failed",
+    507: "Insufficient Storage",
+}
+
+
+def _status_line(code: int) -> str:
+    return f"HTTP/1.1 {code} {_REASONS.get(code, '')}".rstrip()

backend/app/identity/app_passwords.py

@@ -0,0 +1,104 @@
+"""App passwords: one generated password per mail app (SPEC App. D §D.5).
+
+A mail app (Thunderbird, a phone's Mail app) signs in to the hosted mailbox
+over IMAP/SMTP, where no 2FA code can be asked for. It gets a password of its
+own — 16 random letters, shown once — that can be revoked without touching the
+main password or the other apps. The webmail itself never accepts one.
+
+Stored as argon2id hashes (identity/passwords.py), the form the mail server's
+SQL directory reads (§D.3). The hash is of the bare 16 letters: the mail
+server compares exactly what an app sends, so the password is copied and
+entered without the spaces it is shown with.
+"""
+
+from __future__ import annotations
+
+import secrets
+import string
+import uuid
+
+from sqlalchemy import delete, func, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.identity.passwords import hash_password, verify_password
+from app.models import UserAppPassword
+
+LENGTH = 16  # 26^16 ≈ 2^75
+MAX_PER_USER = 25
+NAME_MAX = 60
+_ALPHABET = string.ascii_lowercase
+
+
+def generation_key(user_id: uuid.UUID) -> str:
+    """Redis counter bumped whenever the user's app passwords change: DAV
+    sign-ins cached under the old value stop counting (app/dav/auth.py)."""
+    return f"apppw:gen:{user_id}"
+
+
+async def _changed(user_id: uuid.UUID) -> None:
+    from app.redis_client import get_redis
+
+    await get_redis().incr(generation_key(user_id))
+
+
+class TooMany(Exception):
+    """The user already has MAX_PER_USER app passwords."""
+
+
+def generate() -> str:
+    return "".join(secrets.choice(_ALPHABET) for _ in range(LENGTH))
+
+
+async def list_for(db: AsyncSession, user_id: uuid.UUID) -> list[UserAppPassword]:
+    rows = await db.scalars(
+        select(UserAppPassword)
+        .where(UserAppPassword.user_id == user_id)
+        .order_by(UserAppPassword.created_at.desc())
+    )
+    return list(rows)
+
+
+async def create(db: AsyncSession, user_id: uuid.UUID, name: str) -> tuple[UserAppPassword, str]:
+    """A new app password named ``name``; returns the row and the password
+    itself, which is never available again."""
+    count = await db.scalar(
+        select(func.count()).select_from(UserAppPassword).where(UserAppPassword.user_id == user_id)
+    )
+    if (count or 0) >= MAX_PER_USER:
+        raise TooMany
+    password = generate()
+    row = UserAppPassword(
+        user_id=user_id, name=name.strip()[:NAME_MAX], password_hash=hash_password(password)
+    )
+    db.add(row)
+    await db.commit()
+    return row, password
+
+
+async def revoke(db: AsyncSession, user_id: uuid.UUID, app_password_id: uuid.UUID) -> bool:
+    result = await db.execute(
+        delete(UserAppPassword).where(
+            UserAppPassword.id == app_password_id, UserAppPassword.user_id == user_id
+        )
+    )
+    await db.commit()
+    await _changed(user_id)
+    return bool(result.rowcount)  # type: ignore[attr-defined]
+
+
+async def revoke_all(db: AsyncSession, user_id: uuid.UUID) -> None:
+    """Every app signs in again (the main password was reset)."""
+    await db.execute(delete(UserAppPassword).where(UserAppPassword.user_id == user_id))
+    await db.commit()
+    await _changed(user_id)
+
+
+async def verify(db: AsyncSession, user_id: uuid.UUID, password: str) -> UserAppPassword | None:
+    """The app password ``password`` matches, if any — for the mail server's
+    sign-in and for tests; never for the webmail's own sign-in."""
+    if len(password) != LENGTH:
+        return None
+    for row in await list_for(db, user_id):
+        if verify_password(row.password_hash, password):
+            return row
+    return None

backend/app/identity/routes.py

@@ -16,8 +16,8 @@ from app.api.errors import raise_api_error
 from app.config import get_settings
 from app.db import get_session
 from app.events import get_event_bus
+from app.identity import app_passwords, trusted_devices
 from app.identity import totp as totp_mod
-from app.identity import trusted_devices
 from app.identity.cookies import (
     clear_auth_cookies,
     new_csrf_token,
@@ -34,6 +34,9 @@ from app.identity.reset import (
     request_allowed,
 )
 from app.identity.schemas import (
+    AppPasswordCreatedOut,
+    AppPasswordIn,
+    AppPasswordOut,
     LoginRequest,
     MessageOut,
     PasswordResetCheckIn,
@@ -312,12 +315,68 @@ async def password_reset(body: PasswordResetIn, db: DbSession) -> MessageOut:
     user.password_hash = hash_password(body.password)
     await db.commit()
     await destroy_all_sessions(user.id)  # force re-login everywhere after reset
+    # Mail apps sign in again too: the reset may be the owner taking the account back.
+    await app_passwords.revoke_all(db, user.id)
     # Whoever reset the password may be the owner taking the account back: no
     # device keeps skipping the code on the old trust.
     await trusted_devices.revoke_all(user.id)
     return MessageOut()
 
 
+# --- App passwords (SPEC App. D §D.5) -----------------------------------------
+
+
+def _app_password_out(row: object) -> AppPasswordOut:
+    from app.models import UserAppPassword
+
+    assert isinstance(row, UserAppPassword)
+    return AppPasswordOut(
+        id=str(row.id),
+        name=row.name,
+        created_at=row.created_at.isoformat(),
+        last_used_at=row.last_used_at.isoformat() if row.last_used_at else None,
+    )
+
+
+@router.get("/app-passwords", response_model=list[AppPasswordOut])
+async def list_app_passwords(user: CurrentUser, db: DbSession) -> list[AppPasswordOut]:
+    return [_app_password_out(r) for r in await app_passwords.list_for(db, user.id)]
+
+
+@router.post(
+    "/app-passwords", response_model=AppPasswordCreatedOut, dependencies=[Depends(require_csrf)]
+)
+async def create_app_password(
+    body: AppPasswordIn, user: CurrentUser, db: DbSession
+) -> AppPasswordCreatedOut:
+    """A new password for one mail app. Takes the account password: an app
+    password opens the mailbox without a 2FA code."""
+    if not verify_password(user.password_hash, body.password):
+        raise_api_error(403, "invalid_password", "incorrect password")
+    if not body.name.strip():
+        raise_api_error(400, "invalid_name", "give the app password a name")
+    try:
+        row, password = await app_passwords.create(db, user.id, body.name)
+    except app_passwords.TooMany:
+        raise_api_error(
+            409, "too_many", f"you can have up to {app_passwords.MAX_PER_USER} app passwords"
+        )
+    return AppPasswordCreatedOut(**_app_password_out(row).model_dump(), app_password=password)
+
+
+@router.delete(
+    "/app-passwords/{app_password_id}",
+    response_model=MessageOut,
+    dependencies=[Depends(require_csrf)],
+)
+async def revoke_app_password(
+    app_password_id: uuid.UUID, user: CurrentUser, db: DbSession
+) -> MessageOut:
+    if not await app_passwords.revoke(db, user.id, app_password_id):
+        raise_api_error(404, "not_found", "app password not found")
+    return MessageOut()
+
+
 @router.put("/recovery-email", response_model=UserOut, dependencies=[Depends(require_csrf)])
 async def set_recovery_email(body: RecoveryEmailIn, user: CurrentUser, db: DbSession) -> UserOut:
     """Add, change or remove the recovery address. Takes the password: whoever

backend/app/identity/schemas.py

@@ -63,6 +63,23 @@ class PasswordResetCheckOut(BaseModel):
     totp_required: bool = False
 
 
+class AppPasswordIn(BaseModel):
+    name: str = Field(min_length=1, max_length=60)  # "Thunderbird on laptop"
+    password: str = Field(min_length=1, max_length=1024)  # the account password, to confirm
+
+
+class AppPasswordOut(BaseModel):
+    id: str
+    name: str
+    created_at: str
+    last_used_at: str | None = None
+
+
+class AppPasswordCreatedOut(AppPasswordOut):
+    # The generated password itself: in this answer only, never again.
+    app_password: str
+
+
 class RecoveryEmailIn(BaseModel):
     password: str = Field(min_length=1, max_length=1024)
     # None (or blank) removes the recovery address.

backend/app/models.py

@@ -353,6 +353,22 @@ class SavedSearch(Base):
     pinned: Mapped[bool] = mapped_column(nullable=False, server_default=text("true"))
 
 
+class UserAppPassword(Base):
+    """A password for one mail app (IMAP/SMTP), revocable on its own (§D.5)."""
+
+    __tablename__ = "user_app_passwords"
+
+    id: Mapped[uuid.UUID] = _uuid_pk()
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    name: Mapped[str] = mapped_column(Text, nullable=False)  # "Thunderbird on laptop"
+    password_hash: Mapped[str] = mapped_column(Text, nullable=False)  # argon2id
+    created_at: Mapped[dt.datetime] = _now()
+    # Set by the mail server's sign-in, once there is one.
+    last_used_at: Mapped[dt.datetime | None] = mapped_column(TIMESTAMP(timezone=True))
+
+
 class PushSubscription(Base):
     """A browser or installed app to tell about new mail (Web Push)."""
 

backend/app/plugins/types.py

@@ -112,6 +112,9 @@ class Plugin:
     # Core plugins (calendar, contacts) ship builtin=True: always installed, never
     # offered for removal in the UI, and the uninstall path refuses --drop-data.
     builtin: bool = False
+    # Serves its collections to CalDAV / CardDAV clients (app/dav/provider.py
+    # DavProvider; SPEC Appendix E).
+    dav: Any = None
 
     def __post_init__(self) -> None:
         if not _NAME_RE.fullmatch(self.name):

backend/migrations/versions/0024_app_passwords.py

@@ -0,0 +1,43 @@
+"""app passwords: one password per mail app (SPEC App. D §D.5)
+
+Mail apps (Thunderbird, a phone's Mail app) will sign in to the user's hosted
+mailbox over IMAP/SMTP, where no 2FA code can be asked for. Each app gets its
+own generated password instead, which can be revoked on its own; the main
+password with 2FA stays for the webmail. Stored as argon2id hashes, the form
+the mail server's SQL directory reads (§D.3).
+
+Revision ID: 0024
+Revises: 0023
+Create Date: 2026-10-09
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "0024"
+down_revision: str | None = "0023"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute(
+        """
+        CREATE TABLE user_app_passwords (
+          id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+          user_id uuid NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+          name text NOT NULL,
+          password_hash text NOT NULL,
+          created_at timestamptz NOT NULL DEFAULT now(),
+          last_used_at timestamptz
+        )
+        """
+    )
+    op.execute("CREATE INDEX ix_user_app_passwords_user ON user_app_passwords (user_id)")
+
+
+def downgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS user_app_passwords")

backend/tests/identity/test_app_passwords.py

@@ -0,0 +1,138 @@
+"""App passwords (SPEC App. D §D.5): one generated password per mail app,
+shown once, revocable on its own, never accepted by the webmail's sign-in."""
+
+from __future__ import annotations
+
+import re
+import uuid
+from collections.abc import AsyncIterator
+from dataclasses import dataclass, field
+
+import httpx
+import pytest
+import pytest_asyncio
+from httpx import ASGITransport
+from sqlalchemy import delete, select
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+from app.identity import app_passwords
+from app.identity.passwords import hash_password
+from app.identity.reset import issue_token
+from app.identity.sessions import create_session
+from app.main import create_app
+from app.models import User, UserAppPassword
+
+CSRF = "csrf-token"
+PASSWORD = "hunter2pass"
+
+
+@dataclass
+class Ctx:
+    db: AsyncSession
+    anon: httpx.AsyncClient
+    created: list[uuid.UUID] = field(default_factory=list)
+
+    async def user(self) -> User:
+        user = User(
+            handle=f"ap{uuid.uuid4().hex[:8]}@test.local", password_hash=hash_password(PASSWORD)
+        )
+        self.db.add(user)
+        await self.db.commit()
+        self.created.append(user.id)
+        return user
+
+    async def signed_in(self, user: User) -> httpx.AsyncClient:
+        token = await create_session(user.id, "pytest")
+        return httpx.AsyncClient(
+            transport=ASGITransport(app=create_app()),
+            base_url="http://testserver",
+            cookies={"session": token, "csrf": CSRF},
+            headers={"X-CSRF": CSRF},
+        )
+
+
+@pytest_asyncio.fixture
+async def ctx() -> AsyncIterator[Ctx]:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    db = async_sessionmaker(engine, expire_on_commit=False)()
+    anon = httpx.AsyncClient(transport=ASGITransport(app=create_app()), base_url="http://t")
+    c = Ctx(db=db, anon=anon)
+    try:
+        yield c
+    finally:
+        await anon.aclose()
+        await db.execute(delete(User).where(User.id.in_(c.created)))
+        await db.commit()
+        await db.close()
+        await engine.dispose()
+
+
+async def _create(client: httpx.AsyncClient, name: str, password: str = PASSWORD) -> httpx.Response:
+    return await client.post("/api/auth/app-passwords", json={"name": name, "password": password})
+
+
+async def test_created_once_listed_without_secret_and_revoked(ctx: Ctx) -> None:
+    user = await ctx.user()
+    client = await ctx.signed_in(user)
+
+    assert (await _create(client, "Thunderbird", "wrong")).status_code == 403
+    made = await _create(client, "  Thunderbird on laptop ")
+    assert made.status_code == 200
+    body = made.json()
+    assert body["name"] == "Thunderbird on laptop"
+    assert re.fullmatch(r"[a-z]{16}", body["app_password"])
+
+    listed = (await client.get("/api/auth/app-passwords")).json()
+    assert [a["name"] for a in listed] == ["Thunderbird on laptop"]
+    assert "app_password" not in listed[0] and "password_hash" not in listed[0]
+    assert listed[0]["last_used_at"] is None
+
+    # What the mail server will check: this one matches, nothing else does.
+    row = await app_passwords.verify(ctx.db, user.id, body["app_password"])
+    assert row is not None and str(row.id) == body["id"]
+    assert await app_passwords.verify(ctx.db, user.id, PASSWORD) is None
+    assert await app_passwords.verify(ctx.db, user.id, "a" * 16) is None
+    stored = await ctx.db.scalar(
+        select(UserAppPassword.password_hash).where(UserAppPassword.id == row.id)
+    )
+    assert stored and stored.startswith("$argon2id$") and body["app_password"] not in stored
+
+    # The webmail's own sign-in never takes an app password.
+    login = await ctx.anon.post(
+        "/api/auth/login", json={"handle": user.handle, "password": body["app_password"]}
+    )
+    assert login.status_code == 401
+
+    # Someone else cannot revoke it; its owner can, once.
+    other = await ctx.signed_in(await ctx.user())
+    assert (await other.delete(f"/api/auth/app-passwords/{body['id']}")).status_code == 404
+    assert (await client.delete(f"/api/auth/app-passwords/{body['id']}")).status_code == 200
+    assert (await client.delete(f"/api/auth/app-passwords/{body['id']}")).status_code == 404
+    assert await app_passwords.verify(ctx.db, user.id, body["app_password"]) is None
+    await client.aclose()
+    await other.aclose()
+
+
+async def test_at_most_a_few_per_user(ctx: Ctx, monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(app_passwords, "MAX_PER_USER", 2)
+    client = await ctx.signed_in(await ctx.user())
+    assert (await _create(client, "one")).status_code == 200
+    assert (await _create(client, "two")).status_code == 200
+    third = await _create(client, "three")
+    assert third.status_code == 409 and third.json()["error"]["code"] == "too_many"
+    await client.aclose()
+
+
+async def test_password_reset_revokes_them_all(ctx: Ctx) -> None:
+    user = await ctx.user()
+    client = await ctx.signed_in(user)
+    secret = (await _create(client, "Phone")).json()["app_password"]
+    token = await issue_token(user.id)
+    reset = await ctx.anon.post(
+        "/api/auth/password/reset", json={"token": token, "password": "brandNewPass9"}
+    )
+    assert reset.status_code == 200
+    assert await app_passwords.verify(ctx.db, user.id, secret) is None
+    await client.aclose()

backend/tests/plugins/test_calendar_dav.py

@@ -0,0 +1,231 @@
+"""CalDAV server (SPEC Appendix E): discovery, sign-in with app passwords, and
+two-way changes between DAV clients and the web app on the same rows."""
+
+from __future__ import annotations
+
+import base64
+import re
+import uuid
+from collections.abc import AsyncIterator
+from dataclasses import dataclass
+
+import httpx
+import pytest_asyncio
+from httpx import ASGITransport
+from sqlalchemy import delete, text
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+from app.db import session_scope
+from app.identity import app_passwords
+from app.identity.passwords import hash_password
+from app.identity.sessions import create_session
+from app.main import create_app
+from app.models import User
+
+CAL = "/api/plugins/calendar"
+PROPFIND_ALL = b'<?xml version="1.0"?><d:propfind xmlns:d="DAV:"><d:allprop/></d:propfind>'
+
+EVENT = """BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//test//EN
+BEGIN:VEVENT
+UID:{uid}
+DTSTAMP:20261009T120000Z
+DTSTART;TZID=Europe/Warsaw:20311013T090000
+DTEND;TZID=Europe/Warsaw:20311013T100000
+SUMMARY:{summary}
+X-CLIENT-ONLY:keep me
+BEGIN:VALARM
+ACTION:DISPLAY
+DESCRIPTION:x
+TRIGGER:-PT30M
+END:VALARM
+END:VEVENT
+END:VCALENDAR
+"""
+
+
+@dataclass
+class Ctx:
+    dav: httpx.AsyncClient  # a CalDAV client (Basic, app password)
+    web: httpx.AsyncClient  # the web app (session)
+    anon: httpx.AsyncClient
+    user: User
+    app_password: str
+    app_password_id: uuid.UUID
+    home: str
+    calendar_id: str
+
+
+def _basic(login: str, password: str) -> dict[str, str]:
+    return {"Authorization": "Basic " + base64.b64encode(f"{login}:{password}".encode()).decode()}
+
+
+@pytest_asyncio.fixture
+async def ctx() -> AsyncIterator[Ctx]:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    sm = async_sessionmaker(engine, expire_on_commit=False)
+    async with sm() as s:
+        user = User(
+            handle=f"dav{uuid.uuid4().hex[:8]}@test.local",
+            password_hash=hash_password("account-pw"),
+        )
+        s.add(user)
+        await s.commit()
+    async with session_scope() as db:
+        row, password = await app_passwords.create(db, user.id, "test client")
+    transport = ASGITransport(app=create_app())
+    token = await create_session(user.id, "pytest")
+    web = httpx.AsyncClient(
+        transport=transport,
+        base_url="http://testserver",
+        cookies={"session": token, "csrf": "c"},
+        headers={"X-CSRF": "c"},
+    )
+    calendar_id = (await web.get(f"{CAL}/calendars")).json()[0]["id"]  # bootstraps "Personal"
+    dav = httpx.AsyncClient(
+        transport=transport, base_url="http://testserver", headers=_basic(user.handle, password)
+    )
+    anon = httpx.AsyncClient(transport=transport, base_url="http://testserver")
+    try:
+        yield Ctx(dav, web, anon, user, password, row.id, f"/dav/calendars/{user.id}/", calendar_id)
+    finally:
+        for c in (dav, web, anon):
+            await c.aclose()
+        async with sm() as s:
+            await s.execute(
+                text("DELETE FROM plg_calendar_calendars WHERE user_id = :u"), {"u": str(user.id)}
+            )
+            await s.execute(
+                text("DELETE FROM plg_calendar_dav_changes WHERE user_id = :u"), {"u": str(user.id)}
+            )
+            await s.execute(delete(User).where(User.id == user.id))
+            await s.commit()
+        await engine.dispose()
+
+
+def _sync_report(token: str = "") -> bytes:
+    return (
+        '<?xml version="1.0"?><d:sync-collection xmlns:d="DAV:">'
+        f"<d:sync-token>{token}</d:sync-token><d:sync-level>1</d:sync-level>"
+        "<d:prop><d:getetag/></d:prop></d:sync-collection>"
+    ).encode()
+
+
+async def _sync(c: Ctx, token: str = "") -> tuple[str, str]:
+    r = await c.dav.request("REPORT", f"{c.home}{c.calendar_id}/", content=_sync_report(token))
+    assert r.status_code == 207, r.text
+    new = re.search(r"<d:sync-token>([^<]+)</d:sync-token>", r.text)
+    assert new
+    return new.group(1), r.text
+
+
+async def test_discovery_and_sign_in(ctx: Ctx) -> None:
+    assert (await ctx.anon.get("/.well-known/caldav")).headers["location"] == "/dav/"
+    assert (await ctx.anon.request("PROPFIND", "/dav/")).status_code == 401
+    # The account password never works here — only app passwords.
+    wrong = await ctx.anon.request(
+        "PROPFIND", "/dav/", headers=_basic(ctx.user.handle, "account-pw")
+    )
+    assert wrong.status_code == 401
+    root = await ctx.dav.request("PROPFIND", "/dav/", headers={"Depth": "0"}, content=PROPFIND_ALL)
+    assert root.status_code == 207 and f"/dav/principals/{ctx.user.id}/" in root.text
+    principal = await ctx.dav.request(
+        "PROPFIND", f"/dav/principals/{ctx.user.id}/", headers={"Depth": "0"}
+    )
+    assert ctx.home in principal.text and "calendar-home-set" in principal.text
+    home = await ctx.dav.request("PROPFIND", ctx.home, headers={"Depth": "1"})
+    assert (
+        home.status_code == 207 and "Personal" in home.text and f"{ctx.calendar_id}/" in home.text
+    )
+    # Someone else's home: refused.
+    other = await ctx.dav.request(
+        "PROPFIND", f"/dav/calendars/{uuid.uuid4()}/", headers={"Depth": "1"}
+    )
+    assert other.status_code == 403
+    # Revoking the app password locks the client out at once (no stale cache).
+    async with session_scope() as db:
+        await app_passwords.revoke(db, ctx.user.id, ctx.app_password_id)
+    assert (await ctx.dav.request("PROPFIND", "/dav/")).status_code == 401
+
+
+async def test_client_and_web_app_see_each_others_changes(ctx: Ctx) -> None:
+    url = f"{ctx.home}{ctx.calendar_id}/review.ics"
+    token0, _ = await _sync(ctx)
+
+    # A client adds an event: the web app shows it, alarm included.
+    put = await ctx.dav.put(
+        url,
+        content=EVENT.format(uid="dav-1@test", summary="Review"),
+        headers={"If-None-Match": "*"},
+    )
+    assert put.status_code == 201
+    etag = put.headers["etag"]
+    events = (
+        await ctx.web.get(
+            f"{CAL}/events", params={"start": "2031-10-13T00:00:00Z", "end": "2031-10-14T00:00:00Z"}
+        )
+    ).json()["events"]
+    assert [(e["summary"], e["reminders"], e["tz"]) for e in events] == [
+        ("Review", [30], "Europe/Warsaw")
+    ]
+    event_id = events[0]["id"]
+    got = await ctx.dav.get(url)
+    assert got.headers["etag"] == etag and "X-CLIENT-ONLY:keep me" in got.text  # verbatim
+    token1, body = await _sync(ctx, token0)
+    assert "review.ics" in body
+
+    # Creating it again, or editing an old version, is refused.
+    again = await ctx.dav.put(
+        url, content=EVENT.format(uid="dav-1@test", summary="x"), headers={"If-None-Match": "*"}
+    )
+    assert again.status_code == 412
+    stale = await ctx.dav.put(
+        url, content=EVENT.format(uid="dav-1@test", summary="x"), headers={"If-Match": '"nope"'}
+    )
+    assert stale.status_code == 412
+
+    # The web app renames it: the client gets the new version (regenerated).
+    assert (
+        await ctx.web.patch(f"{CAL}/events/{event_id}", json={"summary": "Review (web)"})
+    ).status_code == 200
+    token2, body = await _sync(ctx, token1)
+    assert "review.ics" in body and token2 != token1
+    got = await ctx.dav.get(url)
+    assert got.headers["etag"] != etag and "SUMMARY:Review (web)" in got.text
+    assert "TRIGGER:-PT30M" in got.text and "TZID=Europe/Warsaw" in got.text
+
+    # The web app deletes it: the client hears it is gone.
+    assert (await ctx.web.delete(f"{CAL}/events/{event_id}")).status_code == 200
+    _, body = await _sync(ctx, token2)
+    assert "review.ics" in body and "404" in body
+    assert (await ctx.dav.get(url)).status_code == 404
+
+
+async def test_client_delete_and_read_only_calendars(ctx: Ctx) -> None:
+    url = f"{ctx.home}{ctx.calendar_id}/gone.ics"
+    put = await ctx.dav.put(url, content=EVENT.format(uid="dav-2@test", summary="Temp"))
+    assert put.status_code == 201
+    assert (await ctx.dav.delete(url, headers={"If-Match": put.headers["etag"]})).status_code == 204
+    events = (
+        await ctx.web.get(
+            f"{CAL}/events", params={"start": "2031-10-13T00:00:00Z", "end": "2031-10-14T00:00:00Z"}
+        )
+    ).json()["events"]
+    assert events == []
+
+    # A subscribed (read-only) calendar refuses writes.
+    async with session_scope() as db:
+        sub = await db.scalar(
+            text(
+                "INSERT INTO plg_calendar_calendars (user_id, name, kind, read_only) "
+                "VALUES (:u, 'Holidays', 'ics_subscription', true) RETURNING id"
+            ),
+            {"u": str(ctx.user.id)},
+        )
+    ro = await ctx.dav.put(
+        f"{ctx.home}{sub}/x.ics", content=EVENT.format(uid="dav-3@test", summary="x")
+    )
+    assert ro.status_code == 403

backend/tests/plugins/test_contacts_dav.py

@@ -0,0 +1,160 @@
+"""CardDAV server (SPEC Appendix E.4): address books, vCards in and out, groups
+as CATEGORIES, and changes flowing both ways with the web app."""
+
+from __future__ import annotations
+
+import base64
+import re
+import uuid
+from collections.abc import AsyncIterator
+from dataclasses import dataclass
+
+import httpx
+import pytest_asyncio
+from httpx import ASGITransport
+from sqlalchemy import delete, text
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+from app.db import session_scope
+from app.identity import app_passwords
+from app.identity.passwords import hash_password
+from app.identity.sessions import create_session
+from app.main import create_app
+from app.models import User
+
+CON = "/api/plugins/contacts"
+IPHONE_CARD = (
+    "BEGIN:VCARD\r\nVERSION:3.0\r\nPRODID:-//Apple Inc.//iPhone OS 18.0//EN\r\n"
+    "N:Kowalska;Anna;;;\r\nFN:Anna Kowalska\r\nORG:Imaginary Pixels;Compositing\r\n"
+    "item1.EMAIL;type=INTERNET;type=WORK;type=pref:anna@ip.example\r\n"
+    "TEL;type=CELL;type=VOICE:+48 600 100 200\r\nCATEGORIES:Clients\r\n"
+    "X-ABUID:ABC123\r\nUID:card-1\r\nEND:VCARD\r\n"
+)
+
+
+@dataclass
+class Ctx:
+    dav: httpx.AsyncClient
+    web: httpx.AsyncClient
+    user: User
+    home: str
+    book_id: str
+
+
+@pytest_asyncio.fixture
+async def ctx() -> AsyncIterator[Ctx]:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    sm = async_sessionmaker(engine, expire_on_commit=False)
+    async with sm() as s:
+        user = User(
+            handle=f"card{uuid.uuid4().hex[:8]}@test.local", password_hash=hash_password("pw")
+        )
+        s.add(user)
+        await s.commit()
+    async with session_scope() as db:
+        _, password = await app_passwords.create(db, user.id, "test client")
+    transport = ASGITransport(app=create_app())
+    token = await create_session(user.id, "pytest")
+    web = httpx.AsyncClient(
+        transport=transport,
+        base_url="http://testserver",
+        cookies={"session": token, "csrf": "c"},
+        headers={"X-CSRF": "c"},
+    )
+    auth = "Basic " + base64.b64encode(f"{user.handle}:{password}".encode()).decode()
+    dav = httpx.AsyncClient(
+        transport=transport, base_url="http://testserver", headers={"Authorization": auth}
+    )
+    home = f"/dav/addressbooks/{user.id}/"
+    listing = await dav.request("PROPFIND", home, headers={"Depth": "1"})
+    book_id = re.findall(rf"{home}([0-9a-f-]{{36}})/", listing.text)[0]
+    try:
+        yield Ctx(dav, web, user, home, book_id)
+    finally:
+        await dav.aclose()
+        await web.aclose()
+        async with sm() as s:
+            for table in ("plg_contacts_books", "plg_contacts_groups", "plg_contacts_dav_changes"):
+                await s.execute(
+                    text(f"DELETE FROM {table} WHERE user_id = :u"), {"u": str(user.id)}
+                )
+            await s.execute(delete(User).where(User.id == user.id))
+            await s.commit()
+        await engine.dispose()
+
+
+async def _sync(c: Ctx, token: str = "") -> tuple[str, str]:
+    body = (
+        '<?xml version="1.0"?><d:sync-collection xmlns:d="DAV:">'
+        f"<d:sync-token>{token}</d:sync-token><d:sync-level>1</d:sync-level>"
+        "<d:prop><d:getetag/></d:prop></d:sync-collection>"
+    )
+    r = await c.dav.request("REPORT", f"{c.home}{c.book_id}/", content=body)
+    assert r.status_code == 207, r.text
+    m = re.search(r"<d:sync-token>([^<]+)</d:sync-token>", r.text)
+    assert m
+    return m.group(1), r.text
+
+
+async def test_discovery_finds_the_address_book(ctx: Ctx) -> None:
+    principal = await ctx.dav.request(
+        "PROPFIND", f"/dav/principals/{ctx.user.id}/", headers={"Depth": "0"}
+    )
+    assert "addressbook-home-set" in principal.text and ctx.home in principal.text
+    book = await ctx.dav.request("PROPFIND", f"{ctx.home}{ctx.book_id}/", headers={"Depth": "0"})
+    assert "Contacts" in book.text and "addressbook" in book.text
+
+
+async def test_a_phone_contact_and_the_web_app(ctx: Ctx) -> None:
+    url = f"{ctx.home}{ctx.book_id}/ABC123.vcf"
+    token0, _ = await _sync(ctx)
+    put = await ctx.dav.put(url, content=IPHONE_CARD, headers={"If-None-Match": "*"})
+    assert put.status_code == 201
+
+    # The web app shows it, in the group its category named.
+    listed = (await ctx.web.get(f"{CON}/contacts", params={"filter": "all", "q": ""})).json()[
+        "contacts"
+    ]
+    assert [c["display_name"] for c in listed] == ["Anna Kowalska"]
+    contact = (await ctx.web.get(f"{CON}/contacts/{listed[0]['id']}")).json()
+    assert contact["org"] == "Imaginary Pixels" and contact["department"] == "Compositing"
+    assert (
+        contact["emails"][0]["value"] == "anna@ip.example"
+        and contact["phones"][0]["type"] == "mobile"
+    )
+    assert [g["name"] for g in contact["groups"]] == ["Clients"]
+    got = await ctx.dav.get(url)
+    assert got.headers["etag"] == put.headers["etag"] and "X-ABUID:ABC123" in got.text  # verbatim
+    token1, body = await _sync(ctx, token0)
+    assert "ABC123.vcf" in body
+
+    # The web app edits it: the phone gets a regenerated card.
+    edit = dict(contact, display_name="Anna K.", group_ids=[g["id"] for g in contact["groups"]])
+    assert (await ctx.web.put(f"{CON}/contacts/{contact['id']}", json=edit)).status_code == 200
+    token2, body = await _sync(ctx, token1)
+    assert "ABC123.vcf" in body
+    got = await ctx.dav.get(url)
+    assert "FN:Anna K." in got.text and "CATEGORIES:Clients" in got.text
+
+    # Deleting the group changes the contact's CATEGORIES.
+    gid = contact["groups"][0]["id"]
+    assert (await ctx.web.delete(f"{CON}/groups/{gid}")).status_code == 200
+    token3, body = await _sync(ctx, token2)
+    assert "ABC123.vcf" in body and "CATEGORIES" not in (await ctx.dav.get(url)).text
+
+    # Multiget, as phones fetch changed cards.
+    multiget = (
+        '<?xml version="1.0"?><card:addressbook-multiget xmlns:d="DAV:" '
+        'xmlns:card="urn:ietf:params:xml:ns:carddav"><d:prop><d:getetag/><card:address-data/>'
+        f"</d:prop><d:href>{url}</d:href><d:href>{ctx.home}{ctx.book_id}/missing.vcf</d:href>"
+        "</card:addressbook-multiget>"
+    )
+    r = await ctx.dav.request("REPORT", f"{ctx.home}{ctx.book_id}/", content=multiget)
+    assert r.status_code == 207 and "BEGIN:VCARD" in r.text and "404" in r.text
+
+    # Deleted in the web app: gone for the phone.
+    assert (await ctx.web.delete(f"{CON}/contacts/{contact['id']}")).status_code == 200
+    _, body = await _sync(ctx, token3)
+    assert "ABC123.vcf" in body and "404" in body

docker/nginx-app.conf

@@ -47,6 +47,26 @@ location /api/ {
     proxy_buffering off;
 }
 
+# ---- CalDAV / CardDAV (SPEC Appendix E) -----------------------------------
+# Phones, Thunderbird and macOS sync calendars and contacts here, signing in
+# with an app password. The well-known paths are how clients find the server
+# from just a host name.
+location /dav/ {
+    proxy_pass http://webmail_api;
+    proxy_http_version 1.1;
+    proxy_set_header Host              $host;
+    proxy_set_header X-Real-IP         $remote_addr;
+    proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
+    proxy_set_header X-Forwarded-Proto $fwd_proto;
+    proxy_set_header X-Forwarded-Host  $host;
+    proxy_read_timeout 300s;
+}
+location ~ ^/\.well-known/(caldav|carddav)$ {
+    proxy_pass http://webmail_api;
+    proxy_set_header Host              $host;
+    proxy_set_header X-Forwarded-Proto $fwd_proto;
+}
+
 # ---- static -------------------------------------------------------------
 # Vite emits content-hashed filenames into /assets, so they are immutable.
 location /assets/ {

docs/nas-install.md

@@ -596,6 +596,24 @@ then also needs `https://ultimo.email/.well-known/assetlinks.json` naming the
 Android package and its signing-certificate fingerprint — served by nginx
 like any other static file.
 
+### 5.4 Calendars and contacts in other apps (CalDAV / CardDAV)
+
+Ultimo serves each user's calendars and address books to standard apps, which
+sync two-way with the web app: iPhone/iPad and macOS Calendar & Contacts,
+Thunderbird, Android through DAVx⁵, GNOME/Evolution.
+
+- **Server:** `https://ultimo.email/dav/` — most apps also find it from just
+  `ultimo.email` (`/.well-known/caldav`, `/.well-known/carddav`).
+- **User name:** the full Ultimo address. **Password:** an **app password**
+  (Settings → Security → App passwords) — the account password is refused, so
+  2FA cannot be bypassed and a lost device is one revocation away. Settings shows
+  the exact server and user name to type.
+- nginx passes `/dav/` and the two well-known paths to the API (in
+  `docker/nginx-app.conf`). A reverse proxy in front (QNAP, DSM) must pass them
+  too, with the `Authorization` header — the default.
+- HTTPS is required by iOS/macOS for these accounts.
+- Repeated wrong passwords are throttled per address and per IP (15 minutes).
+
 ---
 
 ## 6. Resource usage

frontend/src/lib/api.ts

@@ -2,6 +2,7 @@
 // (SPEC §10.3) and includes cookies for the session (SPEC §6.1).
 
 import type {
+  AppPassword,
   AccountDetail,
   AdminMail,
   AdminSettings,
@@ -242,6 +243,14 @@ export const api = {
       body: JSON.stringify({ password }),
     }),
   sessions: () => apiFetch<SessionInfo[]>("/auth/sessions"),
+  appPasswords: () => apiFetch<AppPassword[]>("/auth/app-passwords"),
+  createAppPassword: (name: string, password: string) =>
+    apiFetch<AppPassword & { app_password: string }>("/auth/app-passwords", {
+      method: "POST",
+      body: JSON.stringify({ name, password }),
+    }),
+  revokeAppPassword: (id: string) =>
+    apiFetch<{ message: string }>(`/auth/app-passwords/${id}`, { method: "DELETE" }),
   revokeSession: (sid: string) =>
     apiFetch<{ status: string }>(`/auth/sessions/${sid}`, { method: "DELETE" }),
 

frontend/src/lib/types.ts

@@ -345,3 +345,11 @@ export interface RemoteDraftOut {
   snippet: string;
   updated_at: string;
 }
+
+/** A password for one mail app (Settings → Security → App passwords). */
+export interface AppPassword {
+  id: string;
+  name: string;
+  created_at: string;
+  last_used_at: string | null;
+}

frontend/src/routes/settings/Settings.tsx

@@ -509,6 +509,189 @@ function OfflineAccessSetting() {
   );
 }
 
+/**
+ * Settings → Security: a password for each mail app (Thunderbird, a phone's
+ * Mail app) — they sign in over IMAP/SMTP, where no 2FA code can be asked for.
+ * The password is shown once, when made; each can be revoked on its own.
+ */
+function AppPasswordsSetting() {
+  const t = useT();
+  const handle = useMe().data?.handle ?? "";
+  const queryClient = useQueryClient();
+  const list = useQuery({ queryKey: ["app-passwords"], queryFn: api.appPasswords });
+  const [creating, setCreating] = useState(false);
+  const [name, setName] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState("");
+  const [made, setMade] = useState<{ name: string; secret: string } | null>(null);
+  const [copied, setCopied] = useState(false);
+
+  const create = useMutation({
+    mutationFn: () => api.createAppPassword(name.trim(), password),
+    onSuccess: (out) => {
+      setMade({ name: out.name, secret: out.app_password });
+      setCreating(false);
+      setName("");
+      setPassword("");
+      setError("");
+      void queryClient.invalidateQueries({ queryKey: ["app-passwords"] });
+    },
+    onError: (e) => setError(e instanceof ApiError ? e.message : String(e)),
+  });
+  const revoke = useMutation({
+    mutationFn: (id: string) => api.revokeAppPassword(id),
+    onSuccess: () => void queryClient.invalidateQueries({ queryKey: ["app-passwords"] }),
+  });
+
+  const copy = async () => {
+    if (!made) return;
+    try {
+      await navigator.clipboard.writeText(made.secret);
+      setCopied(true);
+      window.setTimeout(() => setCopied(false), 2000);
+    } catch {
+      /* the text is on screen to copy by hand */
+    }
+  };
+  const date = (iso: string) => new Date(iso).toLocaleDateString(getDateLocale(), { day: "numeric", month: "short", year: "numeric" });
+
+  return (
+    <div className="space-y-2">
+      <h2 className="text-lg font-semibold">{t("appPasswords.title")}</h2>
+      <p className="text-sm text-app-muted">{t("appPasswords.help")}</p>
+      {/* What to type into a calendar / contacts app (CalDAV / CardDAV, SPEC App. E). */}
+      <div className="space-y-1.5 rounded-lg border border-app-border p-3 text-sm">
+        <p className="font-medium">{t("appPasswords.connectTitle")}</p>
+        <dl className="grid grid-cols-[auto_1fr] gap-x-4 gap-y-1">
+          <dt className="text-app-muted">{t("appPasswords.connectServer")}</dt>
+          <dd className="select-all break-all font-mono text-[13px]">{`${window.location.origin}/dav/`}</dd>
+          <dt className="text-app-muted">{t("appPasswords.connectUser")}</dt>
+          <dd className="select-all break-all font-mono text-[13px]">{handle}</dd>
+          <dt className="text-app-muted">{t("appPasswords.connectPassword")}</dt>
+          <dd className="text-app-muted">{t("appPasswords.connectPasswordValue")}</dd>
+        </dl>
+        <p className="text-xs text-app-faint">{t("appPasswords.connectHint")}</p>
+      </div>
+
+      {made && (
+        <div className="space-y-2 rounded-lg border border-emerald-500/40 bg-emerald-500/5 p-3">
+          <p className="text-sm">{t("appPasswords.madeFor", { name: made.name })}</p>
+          <div className="flex flex-wrap items-center gap-3">
+            {/* Shown in groups of four; copied (and entered) without spaces. */}
+            <code className="select-all rounded bg-app-surface px-3 py-2 font-mono text-lg tracking-wider">
+              {made.secret.match(/.{1,4}/g)?.map((group, i) => (
+                // Spacing only, no characters: copying by hand gives the bare letters.
+                <span key={i} className={i ? "ml-2.5" : ""}>
+                  {group}
+                </span>
+              ))}
+            </code>
+            <button
+              className="rounded border border-app-border px-3 py-1.5 text-sm hover:bg-app-hover"
+              onClick={() => void copy()}
+            >
+              {copied ? t("appPasswords.copied") : t("appPasswords.copy")}
+            </button>
+          </div>
+          <p className="text-xs text-app-muted">{t("appPasswords.onceOnly")}</p>
+          <button className="rounded bg-app-accent px-3 py-1 text-sm text-app-accent-fg" onClick={() => setMade(null)}>
+            {t("appPasswords.done")}
+          </button>
+        </div>
+      )}
+
+      {(list.data ?? []).length > 0 && (
+        <ul className="divide-y divide-app-border rounded-lg border border-app-border">
+          {(list.data ?? []).map((a) => (
+            <li key={a.id} className="flex items-center justify-between gap-3 px-3 py-2 text-sm">
+              <span className="min-w-0">
+                <span className="break-words">{a.name}</span>
+                <span className="block text-xs text-app-faint">
+                  {t("appPasswords.created", { date: date(a.created_at) })} ·{" "}
+                  {a.last_used_at
+                    ? t("appPasswords.lastUsed", { date: date(a.last_used_at) })
+                    : t("appPasswords.neverUsed")}
+                </span>
+              </span>
+              <button
+                className="shrink-0 text-xs text-red-500 disabled:opacity-50"
+                disabled={revoke.isPending}
+                onClick={() => {
+                  if (confirm(t("appPasswords.confirmRevoke", { name: a.name }))) revoke.mutate(a.id);
+                }}
+              >
+                {t("settings.revoke")}
+              </button>
+            </li>
+          ))}
+        </ul>
+      )}
+
+      {creating ? (
+        <form
+          className="space-y-2 rounded-lg border border-app-border p-3"
+          onSubmit={(e) => {
+            e.preventDefault();
+            create.mutate();
+          }}
+        >
+          <label className="block text-sm">
+            <span className="text-app-muted">{t("appPasswords.name")}</span>
+            <input
+              className="mt-1 w-full rounded border border-app-border bg-app-surface px-2 py-1 text-sm"
+              placeholder={t("appPasswords.namePlaceholder")}
+              maxLength={60}
+              value={name}
+              onChange={(e) => setName(e.target.value)}
+              autoFocus
+            />
+          </label>
+          <label className="block text-sm">
+            <span className="text-app-muted">{t("appPasswords.confirmPassword")}</span>
+            <input
+              className="mt-1 w-full rounded border border-app-border bg-app-surface px-2 py-1 text-sm"
+              type="password"
+              autoComplete="current-password"
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+            />
+          </label>
+          {error && <p className="text-sm text-red-500">{error}</p>}
+          <div className="flex gap-2">
+            <button
+              type="submit"
+              className="rounded bg-app-accent px-3 py-1 text-sm text-app-accent-fg disabled:opacity-50"
+              disabled={!name.trim() || !password || create.isPending}
+            >
+              {t("appPasswords.create")}
+            </button>
+            <button
+              type="button"
+              className="px-2 text-sm text-app-muted"
+              onClick={() => {
+                setCreating(false);
+                setError("");
+              }}
+            >
+              {t("common.cancel")}
+            </button>
+          </div>
+        </form>
+      ) : (
+        <button
+          className="rounded border border-app-border px-3 py-1.5 text-sm text-app-fg hover:bg-app-hover"
+          onClick={() => {
+            setMade(null);
+            setCreating(true);
+          }}
+        >
+          {t("appPasswords.new")}
+        </button>
+      )}
+    </div>
+  );
+}
+
 function SecuritySection() {
   const t = useT();
   const queryClient = useQueryClient();
@@ -626,6 +809,8 @@ function SecuritySection() {
         {error && <p className="text-sm text-red-500">{error}</p>}
       </div>
 
+      <AppPasswordsSetting />
+
       <div className="space-y-2">
         <h2 className="text-lg font-semibold">{t("settings.sessions")}</h2>
         <ul className="divide-y divide-app-border rounded-lg border border-app-border">

frontend/vite.config.ts

@@ -26,6 +26,10 @@ export default defineConfig({
         changeOrigin: true,
         ws: true,
       },
+      // CalDAV / CardDAV (SPEC Appendix E), for trying clients against dev.
+      "/dav": { target: "http://127.0.0.1:8000", changeOrigin: true },
+      "/.well-known/caldav": { target: "http://127.0.0.1:8000", changeOrigin: true },
+      "/.well-known/carddav": { target: "http://127.0.0.1:8000", changeOrigin: true },
     },
   },
   test: {

plugins/webmail_plugin_calendar/webmail_plugin_calendar/__init__.py

@@ -12,7 +12,9 @@ from __future__ import annotations
 from pathlib import Path
 
 from app.plugins.sdk import JobSpec, Page, PageNav, Plugin, Slot, UiManifest
+from webmail_plugin_calendar.dav import calendar_dav, prune_changes
 from webmail_plugin_calendar.hook import on_message_new
+from webmail_plugin_calendar.reminders import reminder_job
 from webmail_plugin_calendar.router import router
 from webmail_plugin_calendar.sync import caldav_sync
 
@@ -24,9 +26,17 @@ plugin = Plugin(
     builtin=True,
     # An organizer's cancellation, applied to the calendar as the email arrives.
     hooks={"message.new": on_message_new},
+    jobs=[
         # Refresh connected CalDAV calendars every 15 minutes (also runs on connect).
-    jobs=[JobSpec(func=caldav_sync, schedule="*/15 * * * *")],
+        JobSpec(func=caldav_sync, schedule="*/15 * * * *"),
+        # Event reminders, as notifications on the user's devices.
+        JobSpec(func=reminder_job, schedule="* * * * *", singleton=True),
+        # Trim the CalDAV change log nightly (sync tokens stay valid for 90 days).
+        JobSpec(func=prune_changes, schedule="20 4 * * *"),
+    ],
     router=router,
+    # Calendars served to CalDAV clients — phones, Thunderbird (SPEC App. E).
+    dav=calendar_dav,
     ui_manifest=UiManifest(
         # An invitation received by email, above the message body (iMIP): renders
         # only for a message carrying an .ics, so ordinary mail shows nothing.

plugins/webmail_plugin_calendar/webmail_plugin_calendar/dav.py

@@ -0,0 +1,464 @@
+"""The calendar plugin's CalDAV provider (SPEC App. E.3): the user's calendars
+as CalDAV collections, each event series one resource.
+
+Reads and writes the same rows the web app does, in the user's RLS session, so
+reminders, invitations and the upstream CalDAV write-back (the ``dav_dirty``
+trigger; tombstones on synced calendars) behave as for any other change.
+Change numbers come from ``plg_calendar_dav_changes``, filled by triggers.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import uuid
+from collections import defaultdict
+from datetime import UTC, datetime
+from typing import Any
+
+from sqlalchemy import text
+
+from app.dav.provider import Changes, Collection, DavError, Resource
+from app.plugins.sdk import sdk
+from webmail_plugin_calendar import ical_resource
+from webmail_plugin_calendar.queries import expand_range
+
+_SDK = sdk("calendar")
+_C = "{urn:ietf:params:xml:ns:caldav}"
+
+_EVENT_COLUMNS = (
+    "e.id, e.calendar_id, e.ical_uid, e.recurrence_id, e.sequence, e.summary, e.description, "
+    "e.location, e.dtstart, e.dtend, e.all_day, e.tz, e.rrule, e.exdates, e.status, "
+    "e.organizer, e.attendees, e.my_partstat, e.reminders, e.color, e.show_as, "
+    "e.conference_url, e.modified_at, e.srv_ical, e.srv_ical_ver, "
+    "plg_calendar_dav_name(e) AS dav_name"
+)
+
+
+class CalendarDav:
+    kind = "calendar"
+    content_type = "text/calendar; charset=utf-8"
+    extension = ".ics"
+
+    # -- helpers ---------------------------------------------------------------------
+
+    async def _addresses(self, user_id: uuid.UUID) -> set[str]:
+        return {email.lower() for _, email, _ in await _SDK.accounts.of_user(user_id)}
+
+    async def _calendar(self, s: Any, collection_id: str) -> dict[str, Any]:
+        try:
+            uuid.UUID(collection_id)
+        except ValueError:
+            raise DavError(404) from None
+        row = (
+            (
+                await s.execute(
+                    text("SELECT id, kind, read_only FROM plg_calendar_calendars WHERE id = :id"),
+                    {"id": collection_id},
+                )
+            )
+            .mappings()
+            .first()
+        )
+        if row is None:
+            raise DavError(404)
+        return dict(row)
+
+    async def _rows(
+        self, s: Any, collection_id: str, names: list[str] | None = None
+    ) -> dict[str, list[dict[str, Any]]]:
+        """The live rows of a calendar, by resource name."""
+        where = "e.calendar_id = :cal AND e.dav_deleted = false"
+        params: dict[str, Any] = {"cal": collection_id}
+        if names is not None:
+            if not names:
+                return {}
+            where += " AND plg_calendar_dav_name(e) = ANY(:names)"
+            params["names"] = names
+        rows = (
+            (
+                await s.execute(
+                    text(f"SELECT {_EVENT_COLUMNS} FROM plg_calendar_events e WHERE {where}"),
+                    params,
+                )
+            )
+            .mappings()
+            .all()
+        )
+        out: dict[str, list[dict[str, Any]]] = defaultdict(list)
+        for r in rows:
+            out[r["dav_name"]].append(dict(r))
+        return out
+
+    @staticmethod
+    def _serve(
+        rows: list[dict[str, Any]], addresses: set[str], with_data: bool
+    ) -> tuple[str, str | None]:
+        """(ETag, data) of a resource: the client's own text while the fields are
+        unchanged since it was stored, else generated from the fields."""
+        base = next((r for r in rows if r["recurrence_id"] is None), rows[0])
+        fp = ical_resource.fingerprint(rows)
+        raw = base.get("srv_ical")
+        if raw and base.get("srv_ical_ver") == fp:
+            return "r" + hashlib.sha1(raw.encode()).hexdigest(), raw  # noqa: S324
+        return "g" + fp, ical_resource.build(rows, addresses) if with_data else None
+
+    # -- collections -----------------------------------------------------------------
+
+    async def collections(self, user_id: uuid.UUID) -> list[Collection]:
+        async with _SDK.session(user_id) as s:
+            rows = (
+                (
+                    await s.execute(
+                        text(
+                            "SELECT c.id, c.name, c.color, c.kind, c.read_only, "
+                            "COALESCE((SELECT max(id) FROM plg_calendar_dav_changes d "
+                            "          WHERE d.calendar_id = c.id), 0) AS token "
+                            "FROM plg_calendar_calendars c ORDER BY c.name"
+                        )
+                    )
+                )
+                .mappings()
+                .all()
+            )
+        return [
+            Collection(
+                id=str(r["id"]),
+                displayname=r["name"],
+                sync_token=int(r["token"]),
+                color=r["color"],
+                read_only=bool(r["read_only"]) or r["kind"] not in ("local", "caldav"),
+            )
+            for r in rows
+        ]
+
+    async def create_collection(
+        self, user_id: uuid.UUID, collection_id: str, displayname: str, color: str | None
+    ) -> None:
+        try:
+            cid = uuid.UUID(collection_id)
+        except ValueError:
+            raise DavError(403) from None
+        name = (displayname or "Calendar").strip()[:100]
+        async with _SDK.session(user_id) as s:
+            taken = {
+                str(n).lower()
+                for n in (
+                    await s.execute(text("SELECT name FROM plg_calendar_calendars"))
+                ).scalars()
+            }
+            base, n = name, 2
+            while name.lower() in taken:  # names are unique per user
+                name, n = f"{base} ({n})", n + 1
+            await s.execute(
+                text(
+                    "INSERT INTO plg_calendar_calendars (id, user_id, name, color, kind) "
+                    "VALUES (:id, :u, :name, :color, 'local')"
+                ),
+                {
+                    "id": str(cid),
+                    "u": str(user_id),
+                    "name": name,
+                    "color": _color(color) or "#3b82f6",
+                },
+            )
+
+    async def update_collection(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        *,
+        displayname: str | None = None,
+        color: str | None = None,
+        description: str | None = None,
+    ) -> None:
+        sets, params = [], {"id": collection_id}
+        if displayname:
+            sets.append("name = :name")
+            params["name"] = displayname.strip()[:100]
+        if color and _color(color):
+            sets.append("color = :color")
+            params["color"] = _color(color) or ""
+        if not sets:
+            return
+        async with _SDK.session(user_id) as s:
+            await self._calendar(s, collection_id)
+            try:
+                await s.execute(
+                    text(f"UPDATE plg_calendar_calendars SET {', '.join(sets)} WHERE id = :id"),
+                    params,
+                )
+            except Exception as err:  # noqa: BLE001 - a duplicate name
+                raise DavError(409) from err
+
+    async def delete_collection(self, user_id: uuid.UUID, collection_id: str) -> None:
+        async with _SDK.session(user_id) as s:
+            cal = await self._calendar(s, collection_id)
+            if cal["kind"] != "local":
+                raise DavError(403)
+            count = await s.scalar(
+                text("SELECT count(*) FROM plg_calendar_calendars WHERE kind = 'local'")
+            )
+            if (count or 0) <= 1:
+                raise DavError(403)  # the last calendar stays
+            await s.execute(
+                text("DELETE FROM plg_calendar_calendars WHERE id = :id"), {"id": collection_id}
+            )
+
+    # -- resources -------------------------------------------------------------------
+
+    async def resources(self, user_id: uuid.UUID, collection_id: str) -> list[Resource]:
+        return await self._get(user_id, collection_id, None, with_data=False)
+
+    async def get(
+        self, user_id: uuid.UUID, collection_id: str, names: list[str] | None
+    ) -> list[Resource]:
+        return await self._get(user_id, collection_id, names, with_data=True)
+
+    async def _get(
+        self, user_id: uuid.UUID, collection_id: str, names: list[str] | None, *, with_data: bool
+    ) -> list[Resource]:
+        addresses = await self._addresses(user_id) if with_data else set()
+        async with _SDK.session(user_id) as s:
+            await self._calendar(s, collection_id)
+            by_name = await self._rows(s, collection_id, names)
+        out = []
+        for name, rows in by_name.items():
+            etag, data = self._serve(rows, addresses, with_data)
+            out.append(Resource(name=name, etag=etag, data=data))
+        return out
+
+    async def put(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        name: str,
+        data: str,
+        *,
+        if_match: str | None,
+        if_none_match: bool,
+    ) -> tuple[str, bool]:
+        addresses = await self._addresses(user_id)
+        settings = await _SDK.accounts.settings_of(user_id)
+        try:
+            new_rows = ical_resource.parse(data, addresses, str(settings.get("tz") or "UTC"))
+        except ical_resource.InvalidResource as err:
+            raise DavError(400, str(err), condition=f"{_C}valid-calendar-data") from err
+        uid = new_rows[0]["ical_uid"]
+        async with _SDK.session(user_id) as s:
+            cal = await self._calendar(s, collection_id)
+            if cal["read_only"] or cal["kind"] not in ("local", "caldav"):
+                raise DavError(403)
+            existing = (await self._rows(s, collection_id, [name])).get(name)
+            if existing:
+                etag, _ = self._serve(existing, addresses, False)
+                if if_none_match:
+                    raise DavError(412)
+                if if_match and if_match != "*" and if_match != etag:
+                    raise DavError(412)
+                if existing[0]["ical_uid"] != uid:
+                    raise DavError(400, condition=f"{_C}no-uid-conflict")
+            else:
+                if if_match:
+                    raise DavError(412)
+                clash = await s.scalar(
+                    text(
+                        "SELECT plg_calendar_dav_name(e) FROM plg_calendar_events e "
+                        "WHERE calendar_id = :cal AND ical_uid = :uid "
+                        "AND dav_deleted = false LIMIT 1"
+                    ),
+                    {"cal": collection_id, "uid": uid},
+                )
+                if clash and clash != name:
+                    raise DavError(409, condition=f"{_C}no-uid-conflict")
+            keep: list[str] = []
+            for r in new_rows:
+                params = {
+                    "u": str(user_id),
+                    "cal": collection_id,
+                    "uid": uid,
+                    "rid": r["recurrence_id"],
+                    "seq": r["sequence"],
+                    "sum": r["summary"],
+                    "desc": r["description"],
+                    "loc": r["location"],
+                    "start": r["dtstart"],
+                    "end": r["dtend"],
+                    "allday": r["all_day"],
+                    "tz": r["tz"],
+                    "rrule": r["rrule"],
+                    "ex": r["exdates"],
+                    "status": r["status"],
+                    "org": json.dumps(r["organizer"]) if r["organizer"] else None,
+                    "att": json.dumps(r["attendees"]),
+                    "mine": r["my_partstat"],
+                    "rem": r["reminders"],
+                    "color": r["color"],
+                    "showas": r["show_as"],
+                    "conf": r["conference_url"],
+                    "name": name,
+                }
+                row_id = await s.scalar(
+                    text(
+                        "INSERT INTO plg_calendar_events (user_id, calendar_id, ical_uid, "
+                        " recurrence_id, sequence, summary, description, location, dtstart, dtend, "
+                        " all_day, tz, rrule, exdates, status, organizer, attendees, my_partstat, "
+                        " reminders, color, show_as, conference_url, srv_name) "
+                        "VALUES (:u, :cal, :uid, :rid, :seq, :sum, :desc, :loc, :start, :end, "
+                        " :allday, :tz, :rrule, :ex, :status, CAST(:org AS jsonb), "
+                        " CAST(:att AS jsonb), :mine, :rem, :color, :showas, :conf, :name) "
+                        "ON CONFLICT (calendar_id, ical_uid, recurrence_id) DO UPDATE SET "
+                        " sequence = EXCLUDED.sequence, summary = EXCLUDED.summary, "
+                        " description = EXCLUDED.description, location = EXCLUDED.location, "
+                        " dtstart = EXCLUDED.dtstart, dtend = EXCLUDED.dtend, "
+                        " all_day = EXCLUDED.all_day, "
+                        " tz = EXCLUDED.tz, rrule = EXCLUDED.rrule, exdates = EXCLUDED.exdates, "
+                        " status = EXCLUDED.status, organizer = EXCLUDED.organizer, "
+                        " attendees = EXCLUDED.attendees, my_partstat = EXCLUDED.my_partstat, "
+                        " reminders = EXCLUDED.reminders, color = EXCLUDED.color, "
+                        " show_as = EXCLUDED.show_as, conference_url = EXCLUDED.conference_url, "
+                        " srv_name = EXCLUDED.srv_name, dav_deleted = false "
+                        "RETURNING id"
+                    ),
+                    params,
+                )
+                keep.append(str(row_id))
+            # Occurrences no longer in the client's version: gone.
+            await self._remove(s, cal, collection_id, uid, keep)
+            # Keep the client's text, with the fingerprint of the fields it gave.
+            stored = (await self._rows(s, collection_id, [name])).get(name, [])
+            fp = ical_resource.fingerprint(stored)
+            base = next((r for r in stored if r["recurrence_id"] is None), stored[0])
+            await s.execute(
+                text(
+                    "UPDATE plg_calendar_events SET srv_ical = :raw, srv_ical_ver = :fp "
+                    "WHERE id = :id"
+                ),
+                {"raw": data, "fp": fp, "id": str(base["id"])},
+            )
+        return "r" + hashlib.sha1(data.encode()).hexdigest(), not existing  # noqa: S324
+
+    async def _remove(
+        self, s: Any, cal: dict[str, Any], collection_id: str, uid: str, keep: list[str]
+    ) -> None:
+        """Delete a UID's rows (all, or those not in ``keep``) — tombstoned on a
+        calendar synced upstream, so the deletion reaches the server too."""
+        where = "calendar_id = :cal AND ical_uid = :uid AND dav_deleted = false"
+        params: dict[str, Any] = {"cal": collection_id, "uid": uid}
+        if keep:
+            where += " AND NOT (id = ANY(CAST(:keep AS uuid[])))"
+            params["keep"] = keep
+        if cal["kind"] == "caldav":
+            await s.execute(
+                text(f"UPDATE plg_calendar_events SET dav_deleted = true WHERE {where}"), params
+            )
+        else:
+            await s.execute(text(f"DELETE FROM plg_calendar_events WHERE {where}"), params)
+
+    async def delete(
+        self, user_id: uuid.UUID, collection_id: str, name: str, *, if_match: str | None
+    ) -> None:
+        async with _SDK.session(user_id) as s:
+            cal = await self._calendar(s, collection_id)
+            if cal["read_only"] or cal["kind"] not in ("local", "caldav"):
+                raise DavError(403)
+            existing = (await self._rows(s, collection_id, [name])).get(name)
+            if not existing:
+                raise DavError(404)
+            if if_match and if_match != "*":
+                etag, _ = self._serve(existing, set(), False)
+                if if_match != etag:
+                    raise DavError(412)
+            await self._remove(s, cal, collection_id, existing[0]["ical_uid"], [])
+
+    async def changes(self, user_id: uuid.UUID, collection_id: str, since: int) -> Changes | None:
+        async with _SDK.session(user_id) as s:
+            await self._calendar(s, collection_id)
+            rows = (
+                (
+                    await s.execute(
+                        text(
+                            "SELECT id, name, deleted FROM plg_calendar_dav_changes "
+                            "WHERE calendar_id = :cal AND id > :since ORDER BY id"
+                        ),
+                        {"cal": collection_id, "since": since},
+                    )
+                )
+                .mappings()
+                .all()
+            )
+            latest = await s.scalar(
+                text(
+                    "SELECT COALESCE(max(id), 0) FROM plg_calendar_dav_changes "
+                    "WHERE calendar_id = :cal"
+                ),
+                {"cal": collection_id},
+            )
+            oldest = await s.scalar(
+                text("SELECT min(id) FROM plg_calendar_dav_changes WHERE calendar_id = :cal"),
+                {"cal": collection_id},
+            )
+        if oldest is not None and since < int(oldest) - 1 and since < int(latest or 0):
+            return None  # older entries were trimmed (prune_changes): resync
+        if since > int(latest or 0):
+            return None  # a token from the future (another server, a restore): resync
+        state: dict[str, bool] = {}
+        for r in rows:
+            if r["name"]:
+                state[r["name"]] = bool(r["deleted"])
+        return Changes(
+            sync_token=int(latest or 0),
+            changed=[n for n, gone in state.items() if not gone],
+            deleted=[n for n, gone in state.items() if gone],
+        )
+
+    async def query(
+        self, user_id: uuid.UUID, collection_id: str, start: datetime | None, end: datetime | None
+    ) -> list[str] | None:
+        if start is None and end is None:
+            return None
+        lo = start or datetime(1900, 1, 1, tzinfo=UTC)
+        hi = end or datetime(2200, 1, 1, tzinfo=UTC)
+        async with _SDK.session(user_id) as s:
+            await self._calendar(s, collection_id)
+            by_name = await self._rows(s, collection_id, None)
+        names = []
+        for name, rows in by_name.items():
+            base: list[Any] = [
+                dict(r, exdates=r["exdates"] or []) for r in rows if r["recurrence_id"] is None
+            ]
+            overrides: list[Any] = [r for r in rows if r["recurrence_id"] is not None]
+            for r in base + overrides:
+                r.setdefault("origin_message_id", None)
+            if expand_range(base, overrides, lo, hi):
+                names.append(name)
+        return names
+
+
+def _color(value: str | None) -> str | None:
+    """A "#rrggbb" colour from a client's ("#rrggbbaa" from Apple)."""
+    if not value:
+        return None
+    v = value.strip()
+    if v.startswith("#") and len(v) in (7, 9):
+        return v[:7].lower()
+    return None
+
+
+calendar_dav = CalendarDav()
+
+
+async def prune_changes(ctx: dict[str, Any]) -> int:
+    """Nightly: drop change-log entries older than 90 days, keeping each
+    collection's newest (its sync token). A client holding an older token is
+    told to resync (``changes`` answers None)."""
+    async with _SDK.public_session() as pub:
+        result = await pub.execute(
+            text(
+                "DELETE FROM plg_calendar_dav_changes d "
+                "WHERE created_at < now() - interval '90 days' "
+                "AND id < (SELECT max(id) FROM plg_calendar_dav_changes k "
+                "          WHERE k.calendar_id = d.calendar_id)"
+            )
+        )
+    return int(result.rowcount or 0)  # type: ignore[attr-defined]

plugins/webmail_plugin_calendar/webmail_plugin_calendar/ical_resource.py

@@ -0,0 +1,310 @@
+"""One event series as a CalDAV resource: iCalendar text <-> event rows
+(SPEC App. E.3).
+
+A resource holds every row of one UID: the series (no ``recurrence_id``) and
+its moved or cancelled occurrences. :func:`build` writes the rows as a
+VCALENDAR — time zones, all-day dates, recurrence, overrides, organizer and
+attendees, alarms from the reminders, the event colour and video link (as X-
+properties a client keeps); :func:`parse` reads what a client PUT back into row
+fields. :func:`fingerprint` summarises the modelled fields, so a client's own
+text can be served back verbatim for as long as they are unchanged.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+from collections.abc import Mapping, Sequence
+from datetime import UTC, date, datetime, timedelta
+from typing import Any
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
+
+Row = Mapping[str, Any]
+
+# The columns a resource is made of (the fingerprint covers exactly these).
+FIELDS = (
+    "ical_uid",
+    "recurrence_id",
+    "sequence",
+    "summary",
+    "description",
+    "location",
+    "dtstart",
+    "dtend",
+    "all_day",
+    "tz",
+    "rrule",
+    "exdates",
+    "status",
+    "organizer",
+    "attendees",
+    "my_partstat",
+    "reminders",
+    "color",
+    "show_as",
+    "conference_url",
+)
+_PARTSTATS = {"needs-action", "accepted", "declined", "tentative", "delegated"}
+
+
+class InvalidResource(ValueError):
+    """Not a calendar object we can store (no VEVENT, several UIDs, …)."""
+
+
+def _zone(name: str | None) -> ZoneInfo:
+    try:
+        return ZoneInfo(name or "UTC")
+    except (ZoneInfoNotFoundError, ValueError):
+        return ZoneInfo("UTC")
+
+
+def _norm(value: Any) -> Any:
+    if isinstance(value, datetime):
+        return value.astimezone(UTC).isoformat()
+    if isinstance(value, date):
+        return value.isoformat()
+    if isinstance(value, list | tuple):
+        return [_norm(v) for v in value]
+    if isinstance(value, dict):
+        return {k: _norm(v) for k, v in sorted(value.items())}
+    return value
+
+
+def fingerprint(rows: Sequence[Row]) -> str:
+    """A digest of the modelled fields of a resource's rows."""
+    items = sorted(
+        ({f: _norm(r.get(f)) for f in FIELDS} for r in rows),
+        key=lambda d: str(d["recurrence_id"] or ""),
+    )
+    return hashlib.sha1(json.dumps(items, sort_keys=True, default=str).encode()).hexdigest()
+
+
+# ---- rows -> iCalendar ----------------------------------------------------------------
+
+
+def _when(value: datetime, all_day: bool, tz: str) -> date | datetime:
+    if all_day:
+        return value.astimezone(UTC).date()
+    zone = _zone(tz)
+    return value.astimezone(zone) if tz and tz != "UTC" else value.astimezone(UTC)
+
+
+def _address(prop_name: str, person: Mapping[str, Any], partstat: str | None = None) -> Any:
+    from icalendar import vCalAddress
+
+    addr = vCalAddress(f"mailto:{person.get('email', '')}")
+    if person.get("name"):
+        addr.params["CN"] = person["name"]
+    if prop_name == "attendee":
+        addr.params["PARTSTAT"] = (partstat or person.get("partstat") or "needs-action").upper()
+        addr.params["ROLE"] = "REQ-PARTICIPANT"
+    return addr
+
+
+def build(rows: Sequence[Row], my_addresses: set[str]) -> str:
+    """The VCALENDAR for one resource's rows (series first, then overrides)."""
+    from icalendar import Alarm, Calendar, Event
+    from icalendar.prop import vRecur
+
+    cal = Calendar()
+    cal.add("prodid", "-//Ultimo//Calendar//EN")
+    cal.add("version", "2.0")
+    cal.add("calscale", "GREGORIAN")
+    ordered = sorted(
+        rows,
+        key=lambda r: (
+            r.get("recurrence_id") is not None,
+            r.get("recurrence_id") or datetime.min.replace(tzinfo=UTC),
+        ),
+    )
+    for r in ordered:
+        ev = Event()
+        all_day = bool(r.get("all_day"))
+        tz = str(r.get("tz") or "UTC")
+        ev.add("uid", r["ical_uid"])
+        stamp = r.get("modified_at") or datetime(2000, 1, 1, tzinfo=UTC)
+        ev.add("dtstamp", stamp.astimezone(UTC))
+        ev.add("last-modified", stamp.astimezone(UTC))
+        ev.add("sequence", int(r.get("sequence") or 0))
+        ev.add("summary", r.get("summary") or "")
+        if r.get("description"):
+            ev.add("description", r["description"])
+        if r.get("location"):
+            ev.add("location", r["location"])
+        ev.add("dtstart", _when(r["dtstart"], all_day, tz))
+        if r.get("dtend") is not None:
+            ev.add("dtend", _when(r["dtend"], all_day, tz))
+        if r.get("recurrence_id") is not None:
+            ev.add("recurrence-id", _when(r["recurrence_id"], all_day, tz))
+        if r.get("rrule") and r.get("recurrence_id") is None:
+            ev.add("rrule", vRecur.from_ical(str(r["rrule"])))
+        for ex in r.get("exdates") or []:
+            ev.add("exdate", _when(ex, all_day, tz))
+        status = str(r.get("status") or "confirmed").upper()
+        if status in ("CONFIRMED", "TENTATIVE", "CANCELLED"):
+            ev.add("status", status)
+        ev.add("transp", "TRANSPARENT" if r.get("show_as") == "free" else "OPAQUE")
+        organizer = r.get("organizer")
+        if isinstance(organizer, dict) and organizer.get("email"):
+            ev.add("organizer", _address("organizer", organizer))
+        for att in r.get("attendees") or []:
+            if not isinstance(att, dict) or not att.get("email"):
+                continue
+            mine = str(att["email"]).lower() in my_addresses
+            ev.add("attendee", _address("attendee", att, r.get("my_partstat") if mine else None))
+        if r.get("conference_url"):
+            ev.add("x-ultimo-conference", r["conference_url"])
+        if r.get("color"):
+            ev.add("x-ultimo-color", r["color"])
+        for minutes in sorted(set(r.get("reminders") or [])):
+            alarm = Alarm()
+            alarm.add("action", "DISPLAY")
+            alarm.add("description", "Reminder")
+            alarm.add("trigger", timedelta(minutes=-int(minutes)))
+            ev.add_component(alarm)
+        cal.add_component(ev)
+    cal.add_missing_timezones()
+    return str(cal.to_ical().decode())
+
+
+# ---- iCalendar -> rows ----------------------------------------------------------------
+
+
+def _aware(value: date | datetime, default_tz: str) -> tuple[datetime, bool, str]:
+    """(instant, all-day, tz name) of a DTSTART-like value."""
+    if not isinstance(value, datetime):
+        return datetime(value.year, value.month, value.day, tzinfo=UTC), True, "UTC"
+    if value.tzinfo is None:  # floating: the user's own zone
+        zone = _zone(default_tz)
+        return value.replace(tzinfo=zone), False, default_tz or "UTC"
+    name = getattr(value.tzinfo, "key", None) or getattr(value.tzinfo, "zone", None) or ""
+    try:
+        ZoneInfo(str(name))
+    except (ZoneInfoNotFoundError, ValueError):
+        name = "UTC"
+    return value, False, str(name) or "UTC"
+
+
+def _person(prop: Any) -> dict[str, str] | None:
+    if prop is None:
+        return None
+    email = str(prop)
+    if email.lower().startswith("mailto:"):
+        email = email[7:]
+    email = email.strip().lower()
+    if not email:
+        return None
+    name = str(prop.params.get("CN", "")).strip() if hasattr(prop, "params") else ""
+    return {"email": email, "name": "" if name.lower() == email else name}
+
+
+def _list(value: Any) -> list[Any]:
+    if value is None:
+        return []
+    return value if isinstance(value, list) else [value]
+
+
+def _reminders(comp: Any, start: datetime) -> list[int]:
+    out: set[int] = set()
+    for alarm in comp.walk("VALARM"):
+        trigger = alarm.get("trigger")
+        if trigger is None:
+            continue
+        value = trigger.dt
+        if isinstance(value, timedelta):
+            if str(trigger.params.get("RELATED", "START")).upper() != "START":
+                continue
+            minutes = int(-value.total_seconds() // 60)
+        elif isinstance(value, datetime):
+            minutes = int((start - value.astimezone(UTC)).total_seconds() // 60)
+        else:
+            continue
+        if 0 <= minutes <= 60 * 24 * 28:
+            out.add(minutes)
+    return sorted(out)
+
+
+def parse(ics: str, my_addresses: set[str], default_tz: str) -> list[dict[str, Any]]:
+    """The rows a client's VCALENDAR describes (one UID). Raises InvalidResource."""
+    from icalendar import Calendar
+
+    try:
+        cal = Calendar.from_ical(ics)
+    except Exception as err:  # noqa: BLE001 - any parse failure: not valid calendar data
+        raise InvalidResource(str(err)) from err
+    events = list(cal.walk("VEVENT"))
+    if not events:
+        raise InvalidResource("no VEVENT")
+    uids = {str(e.get("uid") or "") for e in events}
+    if len(uids) != 1 or "" in uids:
+        raise InvalidResource("one UID per resource")
+    rows: list[dict[str, Any]] = []
+    for comp in events:
+        start_prop = comp.get("dtstart")
+        if start_prop is None:
+            raise InvalidResource("VEVENT without DTSTART")
+        dtstart, all_day, tz = _aware(start_prop.dt, default_tz)
+        end_prop = comp.get("dtend")
+        if end_prop is not None:
+            dtend = _aware(end_prop.dt, tz)[0]
+        elif comp.get("duration") is not None:
+            dtend = dtstart + comp.get("duration").dt
+        else:
+            dtend = dtstart + (timedelta(days=1) if all_day else timedelta(0))
+        rid_prop = comp.get("recurrence-id")
+        rrule = comp.get("rrule")
+        exdates: list[datetime] = []
+        for ex in _list(comp.get("exdate")):
+            for d in getattr(ex, "dts", []):
+                exdates.append(_aware(d.dt, tz)[0])
+        organizer = _person(comp.get("organizer"))
+        attendees = []
+        my_partstat = None
+        for prop in _list(comp.get("attendee")):
+            who = _person(prop)
+            if who is None:
+                continue
+            stat = str(prop.params.get("PARTSTAT", "NEEDS-ACTION")).lower()
+            who["partstat"] = stat if stat in _PARTSTATS else "needs-action"
+            if who["email"] in my_addresses:
+                my_partstat = who["partstat"]
+            attendees.append(who)
+        conference = ""
+        for key in ("x-ultimo-conference", "x-google-conference", "conference", "url"):
+            value = comp.get(key)
+            if value and str(value).startswith(("https://", "http://")):
+                conference = str(value)
+                break
+        color = str(comp.get("x-ultimo-color") or "") or None
+        status = str(comp.get("status") or "confirmed").lower()
+        rows.append(
+            {
+                "ical_uid": str(comp.get("uid")),
+                "recurrence_id": _aware(rid_prop.dt, tz)[0] if rid_prop is not None else None,
+                "sequence": int(comp.get("sequence") or 0),
+                "summary": str(comp.get("summary") or ""),
+                "description": str(comp.get("description") or ""),
+                "location": str(comp.get("location") or ""),
+                "dtstart": dtstart,
+                "dtend": dtend,
+                "all_day": all_day,
+                "tz": tz,
+                "rrule": rrule.to_ical().decode()
+                if rrule is not None and rid_prop is None
+                else None,
+                "exdates": exdates,
+                "status": status
+                if status in ("confirmed", "tentative", "cancelled")
+                else "confirmed",
+                "organizer": organizer,
+                "attendees": attendees,
+                "my_partstat": my_partstat,
+                "reminders": _reminders(comp, dtstart.astimezone(UTC)),
+                "color": color,
+                "show_as": "free"
+                if str(comp.get("transp") or "").upper() == "TRANSPARENT"
+                else "busy",
+                "conference_url": conference,
+            }
+        )
+    return rows

plugins/webmail_plugin_calendar/webmail_plugin_calendar/migrations/versions/0008_dav_server.py

@@ -0,0 +1,154 @@
+"""calendar: serve calendars to CalDAV clients (SPEC Appendix E.3)
+
+* ``srv_name`` — the resource name a CalDAV client stored the event under (NULL:
+  derived from the UID, ``md5(uid).ics``);
+* ``srv_ical`` / ``srv_ical_ver`` — the iCalendar text a client PUT, served back
+  verbatim while the event's fields still match (``srv_ical_ver`` is their
+  fingerprint when it was stored);
+* ``modified_at`` — when the row last changed (LAST-MODIFIED, DTSTAMP);
+* ``plg_calendar_dav_changes`` — every change to an event or a calendar, numbered:
+  a calendar's sync token / CTag is its latest number, and a client's token
+  says which changes it has seen. Filled by triggers, so every write path
+  counts — the web app, invitations by email, upstream CalDAV sync, DAV clients.
+
+Revision ID: calendar0008
+Revises: calendar0007
+Create Date: 2026-10-09
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+from app.plugins.rls import enable_rls
+
+revision: str = "calendar0008"
+down_revision: str | None = "calendar0007"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute("ALTER TABLE plg_calendar_events ADD COLUMN srv_name text")
+    op.execute("ALTER TABLE plg_calendar_events ADD COLUMN srv_ical text")
+    op.execute("ALTER TABLE plg_calendar_events ADD COLUMN srv_ical_ver text")
+    op.execute(
+        "ALTER TABLE plg_calendar_events ADD COLUMN modified_at timestamptz NOT NULL DEFAULT now()"
+    )
+    op.execute(
+        "CREATE INDEX ix_plg_calendar_events_cal_uid ON plg_calendar_events (calendar_id, ical_uid)"
+    )
+    op.execute(
+        """
+        CREATE TABLE plg_calendar_dav_changes (
+            id bigserial PRIMARY KEY,
+            user_id uuid NOT NULL,
+            calendar_id uuid NOT NULL,
+            name text,                      -- NULL: the calendar itself changed
+            deleted boolean NOT NULL DEFAULT false,
+            created_at timestamptz NOT NULL DEFAULT now()
+        )
+        """
+    )
+    op.execute(
+        "CREATE INDEX ix_plg_calendar_dav_changes_cal ON plg_calendar_dav_changes (calendar_id, id)"
+    )
+    enable_rls("plg_calendar_dav_changes")
+    op.execute("GRANT USAGE ON SEQUENCE plg_calendar_dav_changes_id_seq TO webmail_plugin")
+
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_calendar_dav_name(e plg_calendar_events) RETURNS text AS $$
+          SELECT COALESCE(e.srv_name, md5(e.ical_uid) || '.ics')
+        $$ LANGUAGE sql IMMUTABLE;
+        """
+    )
+    # Stamp modified_at on every change of a row.
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_calendar_touch() RETURNS trigger AS $$
+        BEGIN
+          NEW.modified_at := now();
+          RETURN NEW;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_calendar_events_touch
+          BEFORE UPDATE ON plg_calendar_events
+          FOR EACH ROW EXECUTE FUNCTION plg_calendar_touch();
+        """
+    )
+    # Log every event change under its resource name. A deleted (or tombstoned)
+    # row only deletes the resource when no live row of that UID is left — an
+    # occurrence removed from a series is a change to the series.
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_calendar_log_change() RETURNS trigger AS $$
+        BEGIN
+          -- The old resource, when this row left it (deleted, tombstoned for an
+          -- upstream CalDAV delete, or moved to another calendar). AFTER the
+          -- statement, so the query sees what is left of the UID.
+          IF TG_OP = 'DELETE'
+             OR (TG_OP = 'UPDATE' AND (NEW.calendar_id <> OLD.calendar_id
+                                       OR (NEW.dav_deleted AND NOT OLD.dav_deleted))) THEN
+            INSERT INTO plg_calendar_dav_changes (user_id, calendar_id, name, deleted)
+              VALUES (OLD.user_id, OLD.calendar_id, plg_calendar_dav_name(OLD),
+                      NOT EXISTS (SELECT 1 FROM plg_calendar_events
+                                   WHERE calendar_id = OLD.calendar_id
+                                     AND ical_uid = OLD.ical_uid AND dav_deleted = false));
+          END IF;
+          -- The resource as it is now.
+          IF TG_OP <> 'DELETE' AND NOT NEW.dav_deleted THEN
+            INSERT INTO plg_calendar_dav_changes (user_id, calendar_id, name, deleted)
+              VALUES (NEW.user_id, NEW.calendar_id, plg_calendar_dav_name(NEW), false);
+          END IF;
+          RETURN NULL;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_calendar_events_log
+          AFTER INSERT OR UPDATE OR DELETE ON plg_calendar_events
+          FOR EACH ROW EXECUTE FUNCTION plg_calendar_log_change();
+        """
+    )
+    # A renamed / recoloured calendar changes its CTag too.
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_calendar_log_calendar() RETURNS trigger AS $$
+        BEGIN
+          INSERT INTO plg_calendar_dav_changes (user_id, calendar_id, name, deleted)
+            VALUES (NEW.user_id, NEW.id, NULL, false);
+          RETURN NULL;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_calendar_calendars_log
+          AFTER INSERT OR UPDATE OF name, color ON plg_calendar_calendars
+          FOR EACH ROW EXECUTE FUNCTION plg_calendar_log_calendar();
+        """
+    )
+
+
+def downgrade() -> None:
+    op.execute("DROP TRIGGER IF EXISTS plg_calendar_calendars_log ON plg_calendar_calendars")
+    op.execute("DROP TRIGGER IF EXISTS plg_calendar_events_log ON plg_calendar_events")
+    op.execute("DROP TRIGGER IF EXISTS plg_calendar_events_touch ON plg_calendar_events")
+    op.execute("DROP FUNCTION IF EXISTS plg_calendar_log_calendar()")
+    op.execute("DROP FUNCTION IF EXISTS plg_calendar_log_change()")
+    op.execute("DROP FUNCTION IF EXISTS plg_calendar_touch()")
+    op.execute("DROP FUNCTION IF EXISTS plg_calendar_dav_name(plg_calendar_events)")
+    op.execute("DROP TABLE IF EXISTS plg_calendar_dav_changes")
+    op.execute("DROP INDEX IF EXISTS ix_plg_calendar_events_cal_uid")
+    for col in ("modified_at", "srv_ical_ver", "srv_ical", "srv_name"):
+        op.execute(f"ALTER TABLE plg_calendar_events DROP COLUMN IF EXISTS {col}")

plugins/webmail_plugin_contacts/webmail_plugin_contacts/__init__.py

@@ -13,7 +13,8 @@ from __future__ import annotations
 
 from pathlib import Path
 
-from app.plugins.sdk import Page, PageNav, Plugin, UiManifest
+from app.plugins.sdk import JobSpec, Page, PageNav, Plugin, UiManifest
+from webmail_plugin_contacts.dav import contacts_dav, prune_changes
 from webmail_plugin_contacts.hook import on_message_sent
 from webmail_plugin_contacts.router import router
 
@@ -25,6 +26,10 @@ plugin = Plugin(
     builtin=True,
     hooks={"message.sent": on_message_sent},
     router=router,
+    # Address books served to CardDAV clients — phones, Thunderbird (SPEC App. E).
+    dav=contacts_dav,
+    # Trim the CardDAV change log nightly (sync tokens stay valid for 90 days).
+    jobs=[JobSpec(func=prune_changes, schedule="25 4 * * *")],
     ui_manifest=UiManifest(
         pages=[
             Page(

plugins/webmail_plugin_contacts/webmail_plugin_contacts/dav.py

@@ -0,0 +1,414 @@
+"""The contacts plugin's CardDAV provider (SPEC App. E.4): address books as
+CardDAV collections, each contact one vCard.
+
+The same rows the web app reads and writes, in the user's RLS session. A
+contact's groups are its CATEGORIES: a client's categories become (and are
+kept in step with) the user's groups. Change numbers come from
+``plg_contacts_dav_changes``, filled by triggers.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import uuid
+from collections import defaultdict
+from datetime import datetime
+from typing import Any
+
+from sqlalchemy import text
+
+from app.dav.provider import Changes, Collection, DavError, Resource
+from app.plugins.sdk import sdk
+from webmail_plugin_contacts import vcard
+
+_SDK = sdk("contacts")
+_CR = "{urn:ietf:params:xml:ns:carddav}"
+
+_COLUMNS = (
+    "c.id, c.book_id, c.vcard_uid, c.name_display, c.name_parts, c.nickname, c.emails, "
+    "c.default_email, c.phones, c.addresses, c.urls, c.org, c.department, c.title, "
+    "c.birthday, c.notes, c.starred, c.updated_at, c.srv_vcard, c.srv_vcard_ver, "
+    "plg_contacts_dav_name(c) AS dav_name"
+)
+
+
+class ContactsDav:
+    kind = "addressbook"
+    content_type = "text/vcard; charset=utf-8"
+    extension = ".vcf"
+
+    async def _book(self, s: Any, book_id: str) -> dict[str, Any]:
+        try:
+            uuid.UUID(book_id)
+        except ValueError:
+            raise DavError(404) from None
+        row = (
+            (
+                await s.execute(
+                    text("SELECT id, kind, read_only FROM plg_contacts_books WHERE id = :id"),
+                    {"id": book_id},
+                )
+            )
+            .mappings()
+            .first()
+        )
+        if row is None:
+            raise DavError(404)
+        return dict(row)
+
+    async def _rows(
+        self, s: Any, book_id: str, names: list[str] | None
+    ) -> dict[str, dict[str, Any]]:
+        where = "c.book_id = :book"
+        params: dict[str, Any] = {"book": book_id}
+        if names is not None:
+            if not names:
+                return {}
+            where += " AND plg_contacts_dav_name(c) = ANY(:names)"
+            params["names"] = names
+        rows = (
+            (
+                await s.execute(
+                    text(f"SELECT {_COLUMNS} FROM plg_contacts_contacts c WHERE {where}"), params
+                )
+            )
+            .mappings()
+            .all()
+        )
+        out = {r["dav_name"]: dict(r) for r in rows}
+        if out:
+            groups: dict[str, list[str]] = defaultdict(list)
+            for cid, name in (
+                await s.execute(
+                    text(
+                        "SELECT gm.contact_id, g.name FROM plg_contacts_group_members gm "
+                        "JOIN plg_contacts_groups g ON g.id = gm.group_id "
+                        "WHERE gm.contact_id = ANY(CAST(:ids AS uuid[])) ORDER BY g.name"
+                    ),
+                    {"ids": [str(r["id"]) for r in out.values()]},
+                )
+            ).all():
+                groups[str(cid)].append(name)
+            for r in out.values():
+                r["groups"] = groups.get(str(r["id"]), [])
+        return out
+
+    @staticmethod
+    def _serve(row: dict[str, Any], with_data: bool) -> tuple[str, str | None]:
+        fp = vcard.fingerprint(row, row.get("groups") or [])
+        raw = row.get("srv_vcard")
+        if raw and row.get("srv_vcard_ver") == fp:
+            return "r" + hashlib.sha1(raw.encode()).hexdigest(), raw  # noqa: S324
+        return "g" + fp, vcard.build(row, row.get("groups") or []) if with_data else None
+
+    # -- collections -----------------------------------------------------------------
+
+    async def collections(self, user_id: uuid.UUID) -> list[Collection]:
+        from webmail_plugin_contacts.router import _ensure_book
+
+        async with _SDK.session(user_id) as s:
+            await _ensure_book(s, user_id)  # a new user's first sync finds "Contacts"
+            rows = (
+                (
+                    await s.execute(
+                        text(
+                            "SELECT b.id, b.name, b.kind, b.read_only, "
+                            "COALESCE((SELECT max(id) FROM plg_contacts_dav_changes d "
+                            "          WHERE d.book_id = b.id), 0) AS token "
+                            "FROM plg_contacts_books b ORDER BY b.name"
+                        )
+                    )
+                )
+                .mappings()
+                .all()
+            )
+        return [
+            Collection(
+                id=str(r["id"]),
+                displayname=r["name"],
+                sync_token=int(r["token"]),
+                read_only=bool(r["read_only"]) or r["kind"] != "local",
+                components=[],
+            )
+            for r in rows
+        ]
+
+    async def create_collection(
+        self, user_id: uuid.UUID, collection_id: str, displayname: str, color: str | None
+    ) -> None:
+        try:
+            bid = uuid.UUID(collection_id)
+        except ValueError:
+            raise DavError(403) from None
+        name = (displayname or "Address book").strip()[:100]
+        async with _SDK.session(user_id) as s:
+            taken = {
+                str(n).lower()
+                for n in (await s.execute(text("SELECT name FROM plg_contacts_books"))).scalars()
+            }
+            base, n = name, 2
+            while name.lower() in taken:
+                name, n = f"{base} ({n})", n + 1
+            await s.execute(
+                text("INSERT INTO plg_contacts_books (id, user_id, name) VALUES (:id, :u, :name)"),
+                {"id": str(bid), "u": str(user_id), "name": name},
+            )
+
+    async def update_collection(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        *,
+        displayname: str | None = None,
+        color: str | None = None,
+        description: str | None = None,
+    ) -> None:
+        if not displayname:
+            return
+        async with _SDK.session(user_id) as s:
+            await self._book(s, collection_id)
+            try:
+                await s.execute(
+                    text("UPDATE plg_contacts_books SET name = :n WHERE id = :id"),
+                    {"n": displayname.strip()[:100], "id": collection_id},
+                )
+            except Exception as err:  # noqa: BLE001 - a duplicate name
+                raise DavError(409) from err
+
+    async def delete_collection(self, user_id: uuid.UUID, collection_id: str) -> None:
+        async with _SDK.session(user_id) as s:
+            book = await self._book(s, collection_id)
+            if book["kind"] != "local":
+                raise DavError(403)
+            count = await s.scalar(text("SELECT count(*) FROM plg_contacts_books"))
+            if (count or 0) <= 1:
+                raise DavError(403)  # the last address book stays
+            await s.execute(
+                text("DELETE FROM plg_contacts_books WHERE id = :id"), {"id": collection_id}
+            )
+
+    # -- resources -------------------------------------------------------------------
+
+    async def resources(self, user_id: uuid.UUID, collection_id: str) -> list[Resource]:
+        return await self._get(user_id, collection_id, None, with_data=False)
+
+    async def get(
+        self, user_id: uuid.UUID, collection_id: str, names: list[str] | None
+    ) -> list[Resource]:
+        return await self._get(user_id, collection_id, names, with_data=True)
+
+    async def _get(
+        self, user_id: uuid.UUID, collection_id: str, names: list[str] | None, *, with_data: bool
+    ) -> list[Resource]:
+        async with _SDK.session(user_id) as s:
+            await self._book(s, collection_id)
+            rows = await self._rows(s, collection_id, names)
+        out = []
+        for name, row in rows.items():
+            etag, data = self._serve(row, with_data)
+            out.append(Resource(name=name, etag=etag, data=data))
+        return out
+
+    async def put(
+        self,
+        user_id: uuid.UUID,
+        collection_id: str,
+        name: str,
+        data: str,
+        *,
+        if_match: str | None,
+        if_none_match: bool,
+    ) -> tuple[str, bool]:
+        try:
+            fields, groups = vcard.parse(data)
+        except vcard.InvalidVCard as err:
+            raise DavError(400, str(err), condition=f"{_CR}valid-address-data") from err
+        async with _SDK.session(user_id) as s:
+            book = await self._book(s, collection_id)
+            if book["read_only"] or book["kind"] != "local":
+                raise DavError(403)
+            existing = (await self._rows(s, collection_id, [name])).get(name)
+            if existing:
+                etag, _ = self._serve(existing, False)
+                if if_none_match or (if_match and if_match != "*" and if_match != etag):
+                    raise DavError(412)
+                if existing["vcard_uid"] != fields["vcard_uid"]:
+                    raise DavError(400, condition=f"{_CR}no-uid-conflict")
+            else:
+                if if_match:
+                    raise DavError(412)
+                clash = await s.scalar(
+                    text(
+                        "SELECT plg_contacts_dav_name(c) FROM plg_contacts_contacts c "
+                        "WHERE book_id = :b AND vcard_uid = :uid"
+                    ),
+                    {"b": collection_id, "uid": fields["vcard_uid"]},
+                )
+                if clash and clash != name:
+                    raise DavError(409, condition=f"{_CR}no-uid-conflict")
+            contact_id = await s.scalar(
+                text(
+                    "INSERT INTO plg_contacts_contacts (user_id, book_id, vcard_uid, name_display, "
+                    " name_parts, nickname, emails, default_email, phones, addresses, urls, org, "
+                    " department, title, birthday, notes, starred, srv_name) "
+                    "VALUES (:u, :b, :uid, :fn, CAST(:n AS jsonb), :nick, CAST(:emails AS jsonb), "
+                    " :def, CAST(:phones AS jsonb), CAST(:adr AS jsonb), CAST(:urls AS jsonb), "
+                    " :org, :dept, :title, :bday, :notes, :star, :name) "
+                    "ON CONFLICT (book_id, vcard_uid) DO UPDATE SET "
+                    " name_display = EXCLUDED.name_display, name_parts = EXCLUDED.name_parts, "
+                    " nickname = EXCLUDED.nickname, emails = EXCLUDED.emails, "
+                    " default_email = EXCLUDED.default_email, phones = EXCLUDED.phones, "
+                    " addresses = EXCLUDED.addresses, urls = EXCLUDED.urls, org = EXCLUDED.org, "
+                    " department = EXCLUDED.department, title = EXCLUDED.title, "
+                    " birthday = EXCLUDED.birthday, notes = EXCLUDED.notes, "
+                    " starred = EXCLUDED.starred, srv_name = EXCLUDED.srv_name "
+                    "RETURNING id"
+                ),
+                {
+                    "u": str(user_id),
+                    "b": collection_id,
+                    "uid": fields["vcard_uid"],
+                    "fn": fields["name_display"],
+                    "n": json.dumps(fields["name_parts"]),
+                    "nick": fields["nickname"],
+                    "emails": json.dumps(fields["emails"]),
+                    "def": fields["default_email"],
+                    "phones": json.dumps(fields["phones"]),
+                    "adr": json.dumps(fields["addresses"]),
+                    "urls": json.dumps(fields["urls"]),
+                    "org": fields["org"],
+                    "dept": fields["department"],
+                    "title": fields["title"],
+                    "bday": fields["birthday"],
+                    "notes": fields["notes"],
+                    "star": fields["starred"],
+                    "name": name,
+                },
+            )
+            await self._set_groups(s, user_id, str(contact_id), groups)
+            stored = (await self._rows(s, collection_id, [name]))[name]
+            fp = vcard.fingerprint(stored, stored.get("groups") or [])
+            await s.execute(
+                text(
+                    "UPDATE plg_contacts_contacts SET srv_vcard = :raw, srv_vcard_ver = :fp "
+                    "WHERE id = :id"
+                ),
+                {"raw": data, "fp": fp, "id": str(contact_id)},
+            )
+        return "r" + hashlib.sha1(data.encode()).hexdigest(), not existing  # noqa: S324
+
+    async def _set_groups(
+        self, s: Any, user_id: uuid.UUID, contact_id: str, names: list[str]
+    ) -> None:
+        """Make the contact's groups exactly ``names`` (creating missing ones)."""
+        ids: list[str] = []
+        for name in names:
+            gid = await s.scalar(
+                text(
+                    "INSERT INTO plg_contacts_groups (user_id, name) VALUES (:u, :n) "
+                    "ON CONFLICT (user_id, name) DO NOTHING RETURNING id"
+                ),
+                {"u": str(user_id), "n": name[:100]},
+            )
+            if gid is None:  # exists already (an update would mark all its members changed)
+                gid = await s.scalar(
+                    text("SELECT id FROM plg_contacts_groups WHERE name = :n"), {"n": name[:100]}
+                )
+            ids.append(str(gid))
+        await s.execute(
+            text(
+                "DELETE FROM plg_contacts_group_members WHERE contact_id = :c "
+                "AND NOT (group_id = ANY(CAST(:ids AS uuid[])))"
+            ),
+            {"c": contact_id, "ids": ids},
+        )
+        for gid in ids:
+            await s.execute(
+                text(
+                    "INSERT INTO plg_contacts_group_members (user_id, group_id, contact_id) "
+                    "VALUES (:u, :g, :c) ON CONFLICT DO NOTHING"
+                ),
+                {"u": str(user_id), "g": gid, "c": contact_id},
+            )
+
+    async def delete(
+        self, user_id: uuid.UUID, collection_id: str, name: str, *, if_match: str | None
+    ) -> None:
+        async with _SDK.session(user_id) as s:
+            book = await self._book(s, collection_id)
+            if book["read_only"] or book["kind"] != "local":
+                raise DavError(403)
+            existing = (await self._rows(s, collection_id, [name])).get(name)
+            if not existing:
+                raise DavError(404)
+            if if_match and if_match != "*" and if_match != self._serve(existing, False)[0]:
+                raise DavError(412)
+            await s.execute(
+                text("DELETE FROM plg_contacts_contacts WHERE id = :id"),
+                {"id": str(existing["id"])},
+            )
+
+    async def changes(self, user_id: uuid.UUID, collection_id: str, since: int) -> Changes | None:
+        async with _SDK.session(user_id) as s:
+            await self._book(s, collection_id)
+            rows = (
+                (
+                    await s.execute(
+                        text(
+                            "SELECT id, name, deleted FROM plg_contacts_dav_changes "
+                            "WHERE book_id = :b AND id > :since ORDER BY id"
+                        ),
+                        {"b": collection_id, "since": since},
+                    )
+                )
+                .mappings()
+                .all()
+            )
+            latest = await s.scalar(
+                text(
+                    "SELECT COALESCE(max(id), 0) FROM plg_contacts_dav_changes WHERE book_id = :b"
+                ),
+                {"b": collection_id},
+            )
+            oldest = await s.scalar(
+                text("SELECT min(id) FROM plg_contacts_dav_changes WHERE book_id = :b"),
+                {"b": collection_id},
+            )
+        if oldest is not None and since < int(oldest) - 1 and since < int(latest or 0):
+            return None  # older entries were trimmed (prune_changes): resync
+        if since > int(latest or 0):
+            return None
+        state: dict[str, bool] = {}
+        for r in rows:
+            if r["name"]:
+                state[r["name"]] = bool(r["deleted"])
+        return Changes(
+            sync_token=int(latest or 0),
+            changed=[n for n, gone in state.items() if not gone],
+            deleted=[n for n, gone in state.items() if gone],
+        )
+
+    async def query(
+        self, user_id: uuid.UUID, collection_id: str, start: datetime | None, end: datetime | None
+    ) -> list[str] | None:
+        return None  # address books: the core returns them all
+
+
+contacts_dav = ContactsDav()
+
+
+async def prune_changes(ctx: dict[str, Any]) -> int:
+    """Nightly: drop change-log entries older than 90 days, keeping each address
+    book's newest (its sync token). A client holding an older token is told to
+    resync (``changes`` answers None)."""
+    async with _SDK.public_session() as pub:
+        result = await pub.execute(
+            text(
+                "DELETE FROM plg_contacts_dav_changes d "
+                "WHERE created_at < now() - interval '90 days' "
+                "AND id < (SELECT max(id) FROM plg_contacts_dav_changes k "
+                "          WHERE k.book_id = d.book_id)"
+            )
+        )
+    return int(result.rowcount or 0)  # type: ignore[attr-defined]

plugins/webmail_plugin_contacts/webmail_plugin_contacts/migrations/versions/0002_dav_server.py

@@ -0,0 +1,175 @@
+"""contacts: serve address books to CardDAV clients (SPEC Appendix E.4)
+
+* ``srv_name`` — the resource name a client stored the contact under (NULL:
+  ``md5(uid).vcf``);
+* ``srv_vcard`` / ``srv_vcard_ver`` — the vCard a client PUT, served back
+  verbatim while the contact's fields (and groups) still match;
+* ``plg_contacts_dav_changes`` — numbered changes per address book (sync token /
+  CTag), filled by triggers: a contact changed, its groups changed (they are
+  its CATEGORIES), a group renamed, a book renamed.
+
+Revision ID: contacts0002
+Revises: contacts0001
+Create Date: 2026-10-09
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+from app.plugins.rls import enable_rls
+
+revision: str = "contacts0002"
+down_revision: str | None = "contacts0001"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    for col in ("srv_name", "srv_vcard", "srv_vcard_ver"):
+        op.execute(f"ALTER TABLE plg_contacts_contacts ADD COLUMN {col} text")
+    op.execute(
+        """
+        CREATE TABLE plg_contacts_dav_changes (
+            id bigserial PRIMARY KEY,
+            user_id uuid NOT NULL,
+            book_id uuid NOT NULL,
+            name text,                      -- NULL: the address book itself changed
+            deleted boolean NOT NULL DEFAULT false,
+            created_at timestamptz NOT NULL DEFAULT now()
+        )
+        """
+    )
+    op.execute(
+        "CREATE INDEX ix_plg_contacts_dav_changes_book ON plg_contacts_dav_changes (book_id, id)"
+    )
+    enable_rls("plg_contacts_dav_changes")
+    op.execute("GRANT USAGE ON SEQUENCE plg_contacts_dav_changes_id_seq TO webmail_plugin")
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_contacts_dav_name(c plg_contacts_contacts) RETURNS text AS $$
+          SELECT COALESCE(c.srv_name, md5(c.vcard_uid) || '.vcf')
+        $$ LANGUAGE sql IMMUTABLE;
+        """
+    )
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_contacts_touch() RETURNS trigger AS $$
+        BEGIN
+          NEW.updated_at := now();
+          RETURN NEW;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_contacts_contacts_touch
+          BEFORE UPDATE ON plg_contacts_contacts
+          FOR EACH ROW EXECUTE FUNCTION plg_contacts_touch();
+        """
+    )
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_contacts_log_change() RETURNS trigger AS $$
+        BEGIN
+          IF TG_OP = 'DELETE' OR (TG_OP = 'UPDATE' AND NEW.book_id <> OLD.book_id) THEN
+            INSERT INTO plg_contacts_dav_changes (user_id, book_id, name, deleted)
+              VALUES (OLD.user_id, OLD.book_id, plg_contacts_dav_name(OLD), true);
+          END IF;
+          IF TG_OP <> 'DELETE' THEN
+            INSERT INTO plg_contacts_dav_changes (user_id, book_id, name, deleted)
+              VALUES (NEW.user_id, NEW.book_id, plg_contacts_dav_name(NEW), false);
+          END IF;
+          RETURN NULL;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_contacts_contacts_log
+          AFTER INSERT OR UPDATE OR DELETE ON plg_contacts_contacts
+          FOR EACH ROW EXECUTE FUNCTION plg_contacts_log_change();
+        """
+    )
+    # Group membership is part of the vCard (CATEGORIES).
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_contacts_log_member() RETURNS trigger AS $$
+        DECLARE
+          m plg_contacts_group_members;
+        BEGIN
+          m := CASE WHEN TG_OP = 'DELETE' THEN OLD ELSE NEW END;
+          INSERT INTO plg_contacts_dav_changes (user_id, book_id, name, deleted)
+            SELECT c.user_id, c.book_id, plg_contacts_dav_name(c), false
+              FROM plg_contacts_contacts c WHERE c.id = m.contact_id;
+          RETURN NULL;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_contacts_group_members_log
+          AFTER INSERT OR DELETE ON plg_contacts_group_members
+          FOR EACH ROW EXECUTE FUNCTION plg_contacts_log_member();
+        """
+    )
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_contacts_log_group() RETURNS trigger AS $$
+        BEGIN
+          INSERT INTO plg_contacts_dav_changes (user_id, book_id, name, deleted)
+            SELECT c.user_id, c.book_id, plg_contacts_dav_name(c), false
+              FROM plg_contacts_group_members gm
+              JOIN plg_contacts_contacts c ON c.id = gm.contact_id
+             WHERE gm.group_id = NEW.id;
+          RETURN NULL;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_contacts_groups_log
+          AFTER UPDATE OF name ON plg_contacts_groups
+          FOR EACH ROW EXECUTE FUNCTION plg_contacts_log_group();
+        """
+    )
+    op.execute(
+        """
+        CREATE OR REPLACE FUNCTION plg_contacts_log_book() RETURNS trigger AS $$
+        BEGIN
+          INSERT INTO plg_contacts_dav_changes (user_id, book_id, name, deleted)
+            VALUES (NEW.user_id, NEW.id, NULL, false);
+          RETURN NULL;
+        END;
+        $$ LANGUAGE plpgsql;
+        """
+    )
+    op.execute(
+        """
+        CREATE TRIGGER plg_contacts_books_log
+          AFTER INSERT OR UPDATE OF name ON plg_contacts_books
+          FOR EACH ROW EXECUTE FUNCTION plg_contacts_log_book();
+        """
+    )
+
+
+def downgrade() -> None:
+    op.execute("DROP TRIGGER IF EXISTS plg_contacts_books_log ON plg_contacts_books")
+    op.execute("DROP TRIGGER IF EXISTS plg_contacts_groups_log ON plg_contacts_groups")
+    op.execute(
+        "DROP TRIGGER IF EXISTS plg_contacts_group_members_log ON plg_contacts_group_members"
+    )
+    op.execute("DROP TRIGGER IF EXISTS plg_contacts_contacts_log ON plg_contacts_contacts")
+    op.execute("DROP TRIGGER IF EXISTS plg_contacts_contacts_touch ON plg_contacts_contacts")
+    for fn in ("log_book", "log_group", "log_member", "log_change", "touch"):
+        op.execute(f"DROP FUNCTION IF EXISTS plg_contacts_{fn}()")
+    op.execute("DROP FUNCTION IF EXISTS plg_contacts_dav_name(plg_contacts_contacts)")
+    op.execute("DROP TABLE IF EXISTS plg_contacts_dav_changes")
+    for col in ("srv_vcard_ver", "srv_vcard", "srv_name"):
+        op.execute(f"ALTER TABLE plg_contacts_contacts DROP COLUMN IF EXISTS {col}")

plugins/webmail_plugin_contacts/webmail_plugin_contacts/vcard.py

@@ -0,0 +1,338 @@
+"""vCard (RFC 2426 v3.0, RFC 6350 v4.0) <-> contact fields (SPEC App. E.4).
+
+:func:`parse` reads a vCard 3.0 or 4.0 a client sent into the columns of
+``plg_contacts_contacts`` (plus its CATEGORIES, which are the user's groups);
+:func:`build` writes a contact as vCard 3.0, which every client reads.
+:func:`fingerprint` summarises the modelled fields, so a client's own text can
+be served back verbatim for as long as they are unchanged.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import re
+from collections.abc import Mapping, Sequence
+from datetime import date, datetime
+from typing import Any
+
+FIELDS = (
+    "vcard_uid",
+    "name_display",
+    "name_parts",
+    "nickname",
+    "emails",
+    "default_email",
+    "phones",
+    "addresses",
+    "urls",
+    "org",
+    "department",
+    "title",
+    "birthday",
+    "notes",
+    "starred",
+)
+
+
+class InvalidVCard(ValueError):
+    pass
+
+
+def fingerprint(row: Mapping[str, Any], groups: Sequence[str]) -> str:
+    data = {f: row.get(f) for f in FIELDS}
+    data["groups"] = sorted(groups, key=str.lower)
+    return hashlib.sha1(json.dumps(data, sort_keys=True, default=str).encode()).hexdigest()
+
+
+# ---- text level -----------------------------------------------------------------------
+
+
+def _unfold(text: str) -> list[str]:
+    lines: list[str] = []
+    for raw in text.replace("\r\n", "\n").replace("\r", "\n").split("\n"):
+        if raw[:1] in (" ", "\t") and lines:
+            lines[-1] += raw[1:]
+        elif raw.strip():
+            lines.append(raw)
+    return lines
+
+
+def _split_unescaped(value: str, sep: str) -> list[str]:
+    parts, cur, esc = [], [], False
+    for ch in value:
+        if esc:
+            cur.append("\\" + ch)
+            esc = False
+        elif ch == "\\":
+            esc = True
+        elif ch == sep:
+            parts.append("".join(cur))
+            cur = []
+        else:
+            cur.append(ch)
+    parts.append("".join(cur))
+    return parts
+
+
+def _unescape(value: str) -> str:
+    return re.sub(r"\\(.)", lambda m: "\n" if m.group(1) in "nN" else m.group(1), value)
+
+
+def _escape(value: str) -> str:
+    return value.replace("\\", "\\\\").replace(";", "\\;").replace(",", "\\,").replace("\n", "\\n")
+
+
+class _Line:
+    def __init__(self, raw: str) -> None:
+        head, sep, value = self._split(raw)
+        if not sep:
+            raise InvalidVCard(f"bad line: {raw[:40]}")
+        bits = _split_params(head)
+        name = bits[0]
+        self.name = name.rsplit(".", 1)[-1].upper()  # "item1.EMAIL" -> EMAIL
+        self.params: dict[str, list[str]] = {}
+        for p in bits[1:]:
+            key, eq, val = p.partition("=")
+            if not eq:  # vCard 2.1-style bare type ("WORK")
+                key, val = "TYPE", key
+            vals = [v.strip('"') for v in val.split(",")]
+            self.params.setdefault(key.upper(), []).extend(v for v in vals if v)
+        self.value = value
+
+    @staticmethod
+    def _split(raw: str) -> tuple[str, str, str]:
+        quoted = False
+        for i, ch in enumerate(raw):
+            if ch == '"':
+                quoted = not quoted
+            elif ch == ":" and not quoted:
+                return raw[:i], ":", raw[i + 1 :]
+        return raw, "", ""
+
+    def types(self) -> set[str]:
+        return {t.lower() for t in self.params.get("TYPE", [])}
+
+    def pref(self) -> bool:
+        return "pref" in self.types() or bool(self.params.get("PREF"))
+
+
+def _split_params(head: str) -> list[str]:
+    out, cur, quoted = [], [], False
+    for ch in head:
+        if ch == '"':
+            quoted = not quoted
+            cur.append(ch)
+        elif ch == ";" and not quoted:
+            out.append("".join(cur))
+            cur = []
+        else:
+            cur.append(ch)
+    out.append("".join(cur))
+    return out
+
+
+# ---- vCard -> fields ------------------------------------------------------------------
+
+
+def _birthday(value: str) -> date | None:
+    v = value.strip()
+    for fmt in ("%Y-%m-%d", "%Y%m%d"):
+        try:
+            return datetime.strptime(v[:10] if "-" in v else v[:8], fmt).date()
+        except ValueError:
+            continue
+    return None  # "--MMDD" (no year) and the like are not kept as a date
+
+
+def parse(text: str) -> tuple[dict[str, Any], list[str]]:
+    """(contact fields, group names) of one vCard. Raises InvalidVCard."""
+    lines = _unfold(text)
+    if not lines or lines[0].strip().upper() != "BEGIN:VCARD":
+        raise InvalidVCard("not a vCard")
+    if sum(1 for line in lines if line.strip().upper() == "BEGIN:VCARD") != 1:
+        raise InvalidVCard("one vCard per resource")
+    row: dict[str, Any] = {
+        "vcard_uid": "",
+        "name_display": "",
+        "name_parts": {"prefix": "", "given": "", "middle": "", "family": "", "suffix": ""},
+        "nickname": "",
+        "emails": [],
+        "default_email": "",
+        "phones": [],
+        "addresses": [],
+        "urls": [],
+        "org": "",
+        "department": "",
+        "title": "",
+        "birthday": None,
+        "notes": "",
+        "starred": False,
+    }
+    groups: list[str] = []
+    for raw in lines[1:]:
+        if raw.strip().upper() == "END:VCARD":
+            break
+        line = _Line(raw)
+        name, value, types = line.name, line.value, line.types()
+        if name == "UID":
+            v = _unescape(value).strip()
+            row["vcard_uid"] = v[9:] if v.lower().startswith("urn:uuid:") else v
+        elif name == "FN":
+            row["name_display"] = _unescape(value).strip()
+        elif name == "N":
+            parts = [_unescape(p).strip() for p in _split_unescaped(value, ";")] + [""] * 5
+            row["name_parts"] = {
+                "family": parts[0],
+                "given": parts[1],
+                "middle": parts[2],
+                "prefix": parts[3],
+                "suffix": parts[4],
+            }
+        elif name == "NICKNAME":
+            row["nickname"] = _unescape(_split_unescaped(value, ",")[0]).strip()
+        elif name == "EMAIL":
+            addr = _unescape(value).strip()
+            if addr.lower().startswith("mailto:"):
+                addr = addr[7:]
+            if addr:
+                kind = "work" if "work" in types else "personal" if "home" in types else "other"
+                row["emails"].append({"value": addr, "type": kind, "pref": line.pref()})
+        elif name == "TEL":
+            number = _unescape(value).strip()
+            if number.lower().startswith("tel:"):
+                number = number[4:]
+            if number:
+                kind = (
+                    "mobile"
+                    if "cell" in types
+                    else "work"
+                    if "work" in types
+                    else "home"
+                    if "home" in types
+                    else "other"
+                )
+                row["phones"].append({"value": number, "type": kind})
+        elif name == "ADR":
+            p = [_unescape(x).strip() for x in _split_unescaped(value, ";")] + [""] * 7
+            street = ", ".join(x for x in (p[1], p[2]) if x)  # extended + street
+            kind = "work" if "work" in types else "home" if "home" in types else "other"
+            if any((street, p[3], p[5], p[6])):
+                row["addresses"].append(
+                    {
+                        "type": kind,
+                        "street": street,
+                        "city": p[3],
+                        "postal_code": p[5],
+                        "country": p[6],
+                    }
+                )
+        elif name == "URL":
+            url = _unescape(value).strip()
+            if url:
+                row["urls"].append({"value": url, "type": "website"})
+        elif name == "ORG":
+            p = [_unescape(x).strip() for x in _split_unescaped(value, ";")] + [""]
+            row["org"], row["department"] = p[0], p[1]
+        elif name == "TITLE":
+            row["title"] = _unescape(value).strip()
+        elif name == "BDAY":
+            row["birthday"] = _birthday(_unescape(value))
+        elif name == "NOTE":
+            row["notes"] = _unescape(value)
+        elif name == "CATEGORIES":
+            groups.extend(
+                g for g in (_unescape(x).strip() for x in _split_unescaped(value, ",")) if g
+            )
+        elif name == "X-ULTIMO-VIP":
+            row["starred"] = value.strip() in ("1", "TRUE", "true")
+    if not row["vcard_uid"]:
+        raise InvalidVCard("UID is required")
+    if not row["name_display"]:
+        n = row["name_parts"]
+        row["name_display"] = (
+            " ".join(
+                x for x in (n["prefix"], n["given"], n["middle"], n["family"], n["suffix"]) if x
+            )
+            or row["org"]
+            or (row["emails"][0]["value"] if row["emails"] else "")
+        )
+    pref = next((e["value"] for e in row["emails"] if e["pref"]), None)
+    row["default_email"] = pref or (row["emails"][0]["value"] if row["emails"] else "")
+    return row, list(dict.fromkeys(groups))
+
+
+# ---- fields -> vCard ------------------------------------------------------------------
+
+
+def _fold(line: str) -> str:
+    """Fold at 75 octets (RFC 6350 §3.2), never inside a UTF-8 character."""
+    out: list[str] = []
+    cur = b""
+    for ch in line:
+        b = ch.encode()
+        if len(cur) + len(b) > (75 if not out else 74):
+            out.append(cur.decode())
+            cur = b""
+        cur += b
+    out.append(cur.decode())
+    return "\r\n ".join(out)
+
+
+def build(row: Mapping[str, Any], groups: Sequence[str]) -> str:
+    """A contact as vCard 3.0."""
+    lines = ["BEGIN:VCARD", "VERSION:3.0", "PRODID:-//Ultimo//Contacts//EN"]
+    lines.append(f"UID:{_escape(str(row['vcard_uid']))}")
+    lines.append(f"FN:{_escape(row.get('name_display') or '')}")
+    n = row.get("name_parts") or {}
+    lines.append(
+        "N:"
+        + ";".join(
+            _escape(str(n.get(k, "") or ""))
+            for k in ("family", "given", "middle", "prefix", "suffix")
+        )
+    )
+    if row.get("nickname"):
+        lines.append(f"NICKNAME:{_escape(row['nickname'])}")
+    if row.get("org") or row.get("department"):
+        lines.append(f"ORG:{_escape(row.get('org') or '')};{_escape(row.get('department') or '')}")
+    if row.get("title"):
+        lines.append(f"TITLE:{_escape(row['title'])}")
+    default = (row.get("default_email") or "").lower()
+    for e in row.get("emails") or []:
+        kind = {"work": "WORK", "personal": "HOME"}.get(e.get("type", ""), "OTHER")
+        pref = (
+            ",pref" if e.get("pref") or (default and e.get("value", "").lower() == default) else ""
+        )
+        lines.append(f"EMAIL;TYPE=INTERNET,{kind}{pref}:{_escape(e.get('value', ''))}")
+    for p in row.get("phones") or []:
+        kind = {"mobile": "CELL", "home": "HOME", "work": "WORK"}.get(p.get("type", ""), "VOICE")
+        lines.append(f"TEL;TYPE={kind}:{_escape(p.get('value', ''))}")
+    for a in row.get("addresses") or []:
+        kind = {"home": "HOME", "work": "WORK"}.get(a.get("type", ""), "OTHER")
+        parts = [
+            "",
+            "",
+            a.get("street", ""),
+            a.get("city", ""),
+            "",
+            a.get("postal_code", ""),
+            a.get("country", ""),
+        ]
+        lines.append(f"ADR;TYPE={kind}:" + ";".join(_escape(str(x or "")) for x in parts))
+    for u in row.get("urls") or []:
+        lines.append(f"URL:{_escape(u.get('value', ''))}")
+    bday = row.get("birthday")
+    if bday:
+        lines.append(f"BDAY:{bday.isoformat() if hasattr(bday, 'isoformat') else bday}")
+    if row.get("notes"):
+        lines.append(f"NOTE:{_escape(row['notes'])}")
+    if groups:
+        lines.append("CATEGORIES:" + ",".join(_escape(g) for g in groups))
+    if row.get("starred"):
+        lines.append("X-ULTIMO-VIP:1")
+    updated = row.get("updated_at")
+    if isinstance(updated, datetime):
+        lines.append(f"REV:{updated.strftime('%Y%m%dT%H%M%SZ')}")
+    lines.append("END:VCARD")
+    return "\r\n".join(_fold(line) for line in lines) + "\r\n"

webmail-client-spec_v1.5.md

@@ -874,6 +874,11 @@ CREATE VIEW mail_principals AS
 ### D.5 External mail clients and 2FA
 If phones/desktop clients may use the mailbox over IMAP/SMTP, a password alone would bypass TOTP. Rule: users with 2FA enabled must use **app passwords** for IMAP/SMTP — a `user_app_passwords` table (argon2id hashes) added to the directory view, plus a Settings screen to create/revoke them. Stalwart's login rate limits / auto-ban on. If external clients are not wanted, IMAP/SMTP submission is exposed only on the Docker network and this section shrinks to nothing.
 
+**App passwords — built (v1.3.37, ahead of D5):** table `user_app_passwords` (migration 0024: `id, user_id, name, password_hash, created_at, last_used_at`), `app/identity/app_passwords.py`, routes `GET/POST /api/auth/app-passwords`, `DELETE /api/auth/app-passwords/{id}`, Settings → Security → App passwords.
+- 16 random lowercase letters (~75 bits), shown once in groups of four, copied and entered **without spaces**: the hash is of the bare letters, because the mail server compares exactly what an app sends.
+- Creating one takes the account password; at most 25 per user; each is revoked on its own; a password reset revokes them all (as Google does). The webmail's own sign-in never accepts one.
+- Still for D2/D5: add the hashes to the directory's secrets query (a user's secrets = `users.password_hash` unless 2FA is on, plus every `user_app_passwords.password_hash`), and set `last_used_at` from the mail server's successful sign-ins.
+
 ### D.6 Storing mail once
 Today the indexer keeps every message in full (raw `.eml` blob + sanitized body in `body_parts` + search index), so external accounts are already a second copy, and with Stalwart both copies would sit on the same disk. Ideas, best first:
 
@@ -912,5 +917,32 @@ Today the indexer keeps every message in full (raw `.eml` blob + sanitized body
 3. May external mail clients (IMAP/SMTP) use these mailboxes?
 4. Ship D1 ahead of the rest?
 
+## Appendix E — CalDAV / CardDAV server (phones, Thunderbird, macOS)
+
+Ultimo serves the calendars and address books it already holds to standard clients — iPhone/iPad and macOS Calendar & Contacts, Thunderbird, Android via DAVx5, GNOME/Evolution — so they sync two-way with the web app. No second store: clients read and write the calendar/contacts plugins' own tables. (Chosen over Stalwart's DAV, which would make Stalwart the store and the plugins its clients, §D.)
+
+### E.1 Shape
+- **Core `app/dav/`** — the protocol: routes, Basic sign-in, discovery, principal, XML (PROPFIND / PROPPATCH / REPORT multistatus), ETag preconditions, sync tokens (RFC 6578). No knowledge of events or contacts.
+- **Providers in the plugins** — `Plugin(dav=...)`: the calendar plugin serves calendar collections (iCalendar, RFC 4791), the contacts plugin address books (vCard, RFC 6352). Interface: list collections; list resources (name + ETag); get; put (If-Match / If-None-Match); delete; changes since a sync token; create / update / delete a collection; calendar time-range query. Each runs in the user's RLS session (`sdk.session`).
+- **URLs** — `/.well-known/caldav`, `/.well-known/carddav` → 301 `/dav/`; principal `/dav/principals/{user_id}/`; homes `/dav/calendars/{user_id}/`, `/dav/addressbooks/{user_id}/`; a collection `…/{collection_id}/`; a resource `…/{name}.ics|.vcf`. nginx proxies `/dav/` and the two well-known paths to the API.
+
+### E.2 Sign-in
+HTTP Basic over HTTPS: the handle (full address or local part) and an **app password** (§D.5) — never the account password, so 2FA cannot be bypassed and each device can be revoked. A successful check is cached briefly (keyed by a hash of the password, invalidated when app passwords change) so a sync's many requests don't each cost an argon2id verify; failures are rate-limited per address and IP. `last_used_at` is set (at most every few minutes).
+
+### E.3 Calendars
+- A **resource** is one iCalendar object per UID: the series plus its moved/cancelled occurrences (`RECURRENCE-ID`). Name: what the client PUT it as, else derived from the UID.
+- **Fidelity:** what a client PUTs is kept verbatim and served back unchanged while the event's modelled fields are still what it said; once the web app (or iMIP, or an upstream sync) changes them, the object is regenerated from the fields — SUMMARY, DESCRIPTION, LOCATION, DTSTART/DTEND with TZID and VTIMEZONE, all-day dates, RRULE, EXDATE, overrides, STATUS, TRANSP, ORGANIZER, ATTENDEEs with PARTSTAT, VALARMs from reminders, COLOR, the video link.
+- **Writes** go through the same columns the web app uses, so reminders, invitations and upstream CalDAV write-back (the `dav_dirty` trigger, tombstones on synced calendars) behave identically. Subscribed (ICS) and read-only calendars are served read-only.
+- **Change tracking** by triggers on the plugin tables (any write path counts) into a per-calendar change log; a calendar's sync token / CTag is its latest change number; deletions are reported by name. Old log entries are pruned; a client holding a pruned token gets `valid-sync-token` and resyncs.
+- REPORTs: `calendar-query` (time-range on VEVENT), `calendar-multiget`, `sync-collection`. MKCALENDAR and PROPPATCH (name, colour) create / restyle local calendars; DELETE of a collection deletes a local calendar.
+
+### E.4 Contacts
+Address books = `plg_contacts_books`; resources = contacts as vCard (3.0 served; 3.0 and 4.0 accepted): FN, N, NICKNAME, EMAIL (type, pref), TEL, ADR, URL, ORG/department, TITLE, BDAY, NOTE, CATEGORIES ↔ groups, the VIP star as an `X-` property. Same fidelity rule (`raw_vcard` kept until the web app edits), same change tracking. REPORTs: `addressbook-query` (basic), `addressbook-multiget`, `sync-collection`.
+
+### E.5 Phases
+- **E1** core + discovery + sign-in + calendars read/write (tested with a CalDAV client library);
+- **E2** vCard read/write + address books;
+- **E3** deployment (nginx, docs: how to add the account on each client), then checks with real devices.
+
 ---
 *End of specification. Ambiguities: prefer the simplest behavior consistent with the invariants in §1, leave a `TODO(spec)` comment, and list open questions in `docs/open-questions.md` rather than guessing silently.*