Add per-device active sessions with revocation (#69)

Replaces the stateless signed-cookie session (bare user_id) with a
real server-side sessions table -- the cookie now just carries an
opaque session id, resolved against the DB on every request. Each
session records IP address (respects X-Forwarded-For), a parsed
device label, and last-seen time (throttled updates, not written on
every request).

New GET/DELETE /api/auth/sessions endpoints and an "Active sessions"
section in Profile settings let a user see every device they're
logged in from and revoke one they don't recognize -- including their
own current session, which just signs them out.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/dependencies.py

@@ -8,6 +8,7 @@ from sqlalchemy.orm import selectinload
 from app.database import get_db
 from app.models import RoomMembership, RoomRole, User
 from app.services.bot_service import resolve_token
+from app.services.session_service import resolve_session
 
 _ROLE_RANK = {RoomRole.member: 0, RoomRole.admin: 1, RoomRole.owner: 2}
 
@@ -29,16 +30,26 @@ async def get_current_user(
         request.state.api_token = token
         return user
 
-    user_id = request.session.get("user_id")
-    if not user_id:
+    session_id = request.session.get("session_id")
+    if not session_id:
         raise HTTPException(status_code=401, detail="Not authenticated")
 
+    # #69: a session row, not a bare user_id -- resolve_session is also
+    # where a revoked session (this endpoint's own DELETE, or another
+    # device's "sign out") actually takes effect, since there's no other
+    # per-request check of that state.
+    session = await resolve_session(db, uuid.UUID(session_id))
+    if session is None:
+        request.session.clear()
+        raise HTTPException(status_code=401, detail="Not authenticated")
+    request.state.session_id = session.id
+
     # Eager-loaded so UserRead.active_custom_theme (app/schemas/user.py) can
     # be read without a MissingGreenlet -- selectinload skips the second
     # query entirely when active_custom_theme_id is null (the common case),
     # so this costs nothing for users who've never set a custom theme.
     user = await db.get(
-        User, uuid.UUID(user_id), options=[selectinload(User.active_custom_theme)]
+        User, session.user_id, options=[selectinload(User.active_custom_theme)]
     )
     if user is None or not user.is_active:
         request.session.clear()

backend/app/models/__init__.py

@@ -15,6 +15,7 @@ from app.models.message_room_reference import MessageRoomReference
 from app.models.password_reset import PasswordReset
 from app.models.push_subscription import PushSubscription
 from app.models.room import Room
+from app.models.session import Session
 from app.models.site_invite import SiteInvite
 from app.models.smtp_settings import SmtpSettings
 from app.models.upload_settings import UploadSettings
@@ -35,6 +36,7 @@ __all__ = [
     "MessageRoomReference",
     "InviteStatus",
     "PasswordReset",
+    "Session",
     "SiteInvite",
     "SmtpSettings",
     "UploadSettings",

backend/app/models/session.py

@@ -0,0 +1,43 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, String, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class Session(Base):
+    __tablename__ = "sessions"
+
+    # #69: the row's own id doubles as the opaque value stored in the
+    # signed session cookie (see app/dependencies.py) -- no separate
+    # generate_token()/hash_token() pair like ApiToken needs. A bearer API
+    # token has to be looked up *by itself* from a plaintext string a bot
+    # pastes into an Authorization header (real leak risk, hence hashing
+    # it at rest); this id only ever travels inside itsdangerous's signed,
+    # tamper-proof cookie payload, so a plain UUID primary key carries the
+    # same security properties the stateless cookie already had before
+    # this table existed.
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
+    user_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), index=True, nullable=False)
+    # 45 chars fits the longest possible IPv6 text representation.
+    ip_address: Mapped[str | None] = mapped_column(String(45))
+    user_agent: Mapped[str | None] = mapped_column(String(500))
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False
+    )
+    # Bumped (throttled, not on every request -- see session_service.py) so
+    # "active sessions" can be sorted/labeled by actual recent use, not just
+    # login time -- a session opened once a week ago and used constantly
+    # since should not look identical to one opened once and abandoned.
+    last_seen_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False
+    )
+    # Null while active. Set on explicit logout or a deliberate "sign out
+    # this device" from another session -- never deleted outright, so a
+    # revoked row still means something if anyone ever needs to ask "was
+    # this session valid at time X."
+    revoked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+
+    user = relationship("User")

backend/app/routers/auth.py

@@ -1,3 +1,5 @@
+import uuid
+
 from fastapi import APIRouter, Depends, File, HTTPException, Query, Request, Response, UploadFile
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
@@ -7,6 +9,7 @@ from app.dependencies import get_current_user
 from app.models import User
 from app.schemas.auth import LoginRequest
 from app.schemas.password import ForgotPasswordRequest, PasswordChange, ResetPasswordComplete
+from app.schemas.session import SessionRead
 from app.schemas.user import ProfileUpdate, UserRead
 from app.services.auth_service import (
     AccountDeactivatedError,
@@ -22,7 +25,15 @@ from app.services.password_service import (
     request_password_reset,
     validate_reset_token,
 )
+from app.services.session_service import (
+    SessionNotFoundError,
+    list_sessions,
+    revoke_session,
+    revoke_session_unchecked,
+    start_session,
+)
 from app.services.upload_settings_service import format_mb, get_upload_settings
+from app.services.user_agent_service import describe_user_agent
 from app.storage import (
     ALLOWED_IMAGE_CONTENT_TYPES,
     InvalidImageError,
@@ -55,12 +66,15 @@ async def login(
     except AccountDeactivatedError:
         raise HTTPException(status_code=401, detail="Account is deactivated")
 
-    request.session["user_id"] = str(user.id)
+    await start_session(request, db, user.id)
     return user
 
 
 @router.post("/logout", status_code=204)
-async def logout(request: Request) -> Response:
+async def logout(request: Request, db: AsyncSession = Depends(get_db)) -> Response:
+    session_id = request.session.get("session_id")
+    if session_id:
+        await revoke_session_unchecked(db, uuid.UUID(session_id))
     request.session.clear()
     return Response(status_code=204)
 
@@ -218,5 +232,37 @@ async def complete_reset_password_endpoint(
     except PasswordResetInvalidError:
         raise HTTPException(status_code=400, detail="This reset link is invalid or has expired")
 
-    request.session["user_id"] = str(user.id)
+    await start_session(request, db, user.id)
     return user
+
+
+@router.get("/sessions", response_model=list[SessionRead])
+async def list_sessions_endpoint(
+    request: Request,
+    current_user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    sessions = await list_sessions(db, current_user.id)
+    return [
+        SessionRead(
+            id=s.id,
+            ip_address=s.ip_address,
+            device_label=describe_user_agent(s.user_agent),
+            created_at=s.created_at,
+            last_seen_at=s.last_seen_at,
+            is_current=s.id == request.state.session_id,
+        )
+        for s in sessions
+    ]
+
+
+@router.delete("/sessions/{session_id}", status_code=204)
+async def revoke_session_endpoint(
+    session_id: uuid.UUID,
+    current_user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    try:
+        await revoke_session(db, current_user.id, session_id)
+    except SessionNotFoundError:
+        raise HTTPException(status_code=404, detail="Session not found")

backend/app/routers/signup.py

@@ -5,6 +5,7 @@ from app.database import get_db
 from app.schemas.site_invite import SignupComplete, SignupValidateRead
 from app.schemas.user import UserRead
 from app.services.auth_service import DuplicateUserError
+from app.services.session_service import start_session
 from app.services.site_invite_service import (
     SiteInviteInvalidError,
     complete_signup,
@@ -39,5 +40,5 @@ async def complete_signup_endpoint(
     except DuplicateUserError:
         raise HTTPException(status_code=409, detail="That username or email is already taken")
 
-    request.session["user_id"] = str(user.id)
+    await start_session(request, db, user.id)
     return user

backend/app/schemas/session.py

@@ -0,0 +1,20 @@
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel
+
+
+class SessionRead(BaseModel):
+    id: uuid.UUID
+    ip_address: str | None
+    # Parsed from the stored user_agent by the router (see
+    # user_agent_service.describe_user_agent) -- not a stored column, so a
+    # future improvement to the parser applies retroactively to old rows
+    # too.
+    device_label: str
+    created_at: datetime
+    last_seen_at: datetime
+    # Whether this is the session the request making this call is itself
+    # authenticated with -- lets the UI mark "this device" and treat
+    # revoking it as a self-logout rather than just another row.
+    is_current: bool

backend/app/services/session_service.py

@@ -0,0 +1,100 @@
+import uuid
+from datetime import datetime, timedelta, timezone
+
+from fastapi import Request
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models import Session
+
+# #69: how stale last_seen_at has to be before a request bothers updating
+# it. get_current_user resolves a session on *every* authenticated
+# request (dozens per minute per active browser tab, between message
+# polling, presence, etc.) -- writing+committing on every single one would
+# turn a read into a write storm for no real benefit, since "active
+# sessions" only needs last-seen accurate to within a few minutes, not to
+# the second.
+LAST_SEEN_THROTTLE = timedelta(minutes=5)
+
+
+class SessionNotFoundError(Exception):
+    pass
+
+
+def get_client_ip(request_or_websocket) -> str | None:
+    # X-Forwarded-For's first entry is the original client -- everything
+    # after it was appended by intermediate proxies. Production runs
+    # behind Nginx Proxy Manager (see backend/README.md's "Admin portal"
+    # section preamble), which sets this; local dev has nothing in front
+    # of the app, so this falls back to the direct peer address.
+    forwarded = request_or_websocket.headers.get("x-forwarded-for")
+    if forwarded:
+        return forwarded.split(",")[0].strip()
+    client = request_or_websocket.client
+    return client.host if client else None
+
+
+async def create_session(
+    db: AsyncSession, user_id: uuid.UUID, ip_address: str | None, user_agent: str | None
+) -> Session:
+    session = Session(user_id=user_id, ip_address=ip_address, user_agent=user_agent)
+    db.add(session)
+    await db.commit()
+    await db.refresh(session)
+    return session
+
+
+async def start_session(request: Request, db: AsyncSession, user_id: uuid.UUID) -> Session:
+    """Every "log this browser in" call site (login, reset-password
+    completion, signup completion) needs the exact same three steps --
+    read the request's IP/UA, create the row, stash its id in the signed
+    cookie -- so this is the one place that combination lives."""
+    session = await create_session(db, user_id, get_client_ip(request), request.headers.get("user-agent"))
+    request.session["session_id"] = str(session.id)
+    return session
+
+
+async def resolve_session(db: AsyncSession, session_id: uuid.UUID) -> Session | None:
+    """Returns the session iff it exists and hasn't been revoked -- the
+    single choke point get_current_user and the WS handshake both go
+    through, so revoking a session (this endpoint or another device's
+    "sign out") takes effect on that session's very next request rather
+    than only once its signed cookie happens to expire."""
+    session = await db.get(Session, session_id)
+    if session is None or session.revoked_at is not None:
+        return None
+
+    now = datetime.now(timezone.utc)
+    if now - session.last_seen_at > LAST_SEEN_THROTTLE:
+        session.last_seen_at = now
+        await db.commit()
+    return session
+
+
+async def list_sessions(db: AsyncSession, user_id: uuid.UUID) -> list[Session]:
+    result = await db.execute(
+        select(Session)
+        .where(Session.user_id == user_id, Session.revoked_at.is_(None))
+        .order_by(Session.last_seen_at.desc())
+    )
+    return list(result.scalars().all())
+
+
+async def revoke_session(db: AsyncSession, user_id: uuid.UUID, session_id: uuid.UUID) -> None:
+    session = await db.get(Session, session_id)
+    if session is None or session.user_id != user_id or session.revoked_at is not None:
+        raise SessionNotFoundError()
+    session.revoked_at = datetime.now(timezone.utc)
+    await db.commit()
+
+
+async def revoke_session_unchecked(db: AsyncSession, session_id: uuid.UUID) -> None:
+    """Logout's own path -- no ownership check needed (a session can only
+    ever log itself out) and silently does nothing for a session that's
+    missing or already revoked, since "sign this browser out" should
+    never itself fail."""
+    session = await db.get(Session, session_id)
+    if session is None or session.revoked_at is not None:
+        return
+    session.revoked_at = datetime.now(timezone.utc)
+    await db.commit()

backend/app/services/user_agent_service.py

@@ -0,0 +1,46 @@
+def describe_user_agent(user_agent: str | None) -> str:
+    """A short, human-readable "Browser on OS" label for the sessions list
+    -- no dependency pulled in for this (the app has stayed on a
+    zero-subdependency-when-possible diet, see MessageContent.tsx's
+    markdown-to-jsx choice), just substring checks against the handful of
+    tokens that actually distinguish the browsers/platforms this app's
+    users run. Order matters: Electron and Edge both also contain
+    "Chrome/", and Chrome-on-iOS/Safari-on-iOS both contain "Safari/", so
+    the more specific token has to be checked first.
+    """
+    if not user_agent:
+        return "Unknown device"
+
+    if "Electron/" in user_agent:
+        browser = "DS Chat Desktop"
+    elif "Edg/" in user_agent:
+        browser = "Edge"
+    elif "OPR/" in user_agent:
+        browser = "Opera"
+    elif "Firefox/" in user_agent:
+        browser = "Firefox"
+    elif "Chrome/" in user_agent:
+        browser = "Chrome"
+    elif "CriOS/" in user_agent:
+        browser = "Chrome"
+    elif "Safari/" in user_agent:
+        browser = "Safari"
+    else:
+        browser = "Unknown browser"
+
+    if "Windows" in user_agent:
+        os_name = "Windows"
+    elif "Mac OS X" in user_agent and ("iPhone" in user_agent or "iPad" in user_agent):
+        os_name = "iOS"
+    elif "Mac OS X" in user_agent:
+        os_name = "macOS"
+    elif "Android" in user_agent:
+        os_name = "Android"
+    elif "Linux" in user_agent:
+        os_name = "Linux"
+    else:
+        os_name = "Unknown OS"
+
+    if browser == "DS Chat Desktop":
+        return f"{browser} ({os_name})"
+    return f"{browser} on {os_name}"

backend/app/ws/chat.py

@@ -25,6 +25,7 @@ from app.services.message_service import (
     toggle_reaction,
 )
 from app.services.room_service import mark_room_read
+from app.services.session_service import resolve_session
 
 router = APIRouter(tags=["ws"])
 
@@ -75,11 +76,15 @@ async def chat_endpoint(websocket: WebSocket, db: AsyncSession = Depends(get_db)
             return
         user, api_token = resolved
     else:
-        user_id_raw = websocket.session.get("user_id")
-        if not user_id_raw:
+        session_id_raw = websocket.session.get("session_id")
+        if not session_id_raw:
             await websocket.close(code=WS_UNAUTHENTICATED)
             return
-        user = await db.get(User, uuid.UUID(user_id_raw))
+        session = await resolve_session(db, uuid.UUID(session_id_raw))
+        if session is None:
+            await websocket.close(code=WS_UNAUTHENTICATED)
+            return
+        user = await db.get(User, session.user_id)
         if user is None or not user.is_active:
             await websocket.close(code=WS_UNAUTHENTICATED)
             return