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/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