92 lines
3.0 KiB
Python
92 lines
3.0 KiB
Python
 
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"""Trusted devices: "don't ask for the 2FA code on this device" (SPEC §6.1).
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Ticking the box at a successful 2FA sign-in stores a random token in Redis
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(``trustdev:{token}`` -> user id) and hands it to the browser in its own
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HttpOnly cookie. A later sign-in to the *same* account from that browser may
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then skip the code — the password is still required. Other accounts signing in
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on the same browser are unaffected.
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The trust lasts TRUST_DAYS and is renewed each time it is used, so a device in
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regular use stays trusted while one left alone for that long has to show a code
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again. A per-user index (``trustdev-user:{user_id}``) lets everything be revoked
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at once: on a password reset, when 2FA is turned off, and when an administrator
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blocks or deletes the account. Signing out does not revoke it — that is the
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point of the box.
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"""
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from __future__ import annotations
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import secrets
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import uuid
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from fastapi import Request, Response
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from app.redis_client import aw, get_redis
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TRUST_DAYS = 90
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_TTL = TRUST_DAYS * 24 * 3600
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_PREFIX = "trustdev:"
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_INDEX = "trustdev-user:"
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COOKIE_SECURE = "__Host-trusted-device"
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COOKIE_INSECURE = "trusted_device"
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def _cookie_name(request: Request) -> str:
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# Same split as the session cookie: the __Host- prefix needs HTTPS.
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return COOKIE_SECURE if request.url.scheme == "https" else COOKIE_INSECURE
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def read_cookie(request: Request) -> str:
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return request.cookies.get(COOKIE_SECURE) or request.cookies.get(COOKIE_INSECURE, "")
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async def trust(request: Request, response: Response, user_id: uuid.UUID) -> None:
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"""Remember this browser for ``user_id`` and set the cookie."""
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token = secrets.token_urlsafe(32)
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redis = get_redis()
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await redis.set(_PREFIX + token, str(user_id), ex=_TTL)
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await aw(redis.sadd(_INDEX + str(user_id), token))
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await redis.expire(_INDEX + str(user_id), _TTL)
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response.set_cookie(
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_cookie_name(request),
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token,
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max_age=_TTL,
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httponly=True,
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secure=request.url.scheme == "https",
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samesite="lax",
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path="/",
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)
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async def is_trusted(request: Request, response: Response, user_id: uuid.UUID) -> bool:
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"""Whether this browser is trusted for ``user_id``; renews the trust if so."""
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token = read_cookie(request)
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if not token:
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return False
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redis = get_redis()
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if await redis.get(_PREFIX + token) != str(user_id):
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return False
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await redis.expire(_PREFIX + token, _TTL)
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await redis.expire(_INDEX + str(user_id), _TTL)
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response.set_cookie(
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_cookie_name(request),
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token,
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max_age=_TTL,
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httponly=True,
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secure=request.url.scheme == "https",
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samesite="lax",
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path="/",
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)
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return True
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async def revoke_all(user_id: uuid.UUID) -> None:
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"""Forget every device trusted for ``user_id``."""
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redis = get_redis()
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index = _INDEX + str(user_id)
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tokens: set[str] = await aw(redis.smembers(index))
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if tokens:
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await redis.delete(*(_PREFIX + t for t in tokens))
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await redis.delete(index)
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