app/auth.py

"""HF OAuth flow — anonymous-first, recognition-only.

When OAUTH_CLIENT_ID is not set (local / unconfigured), all routes degrade
gracefully: /login returns a friendly unavailable response, /me returns
signed_in:false, /logout still clears the session and redirects.

Privacy contract: ONLY hash_uid(sub) is stored in the session.
Never the username, preferred_username, name, or raw sub.
"""
from __future__ import annotations
import os

from authlib.integrations.starlette_client import OAuth
from fastapi import APIRouter, Request
from fastapi.responses import JSONResponse, RedirectResponse

from app.identity import hash_uid


def make_oauth() -> OAuth | None:
    cid = os.environ.get("OAUTH_CLIENT_ID")
    if not cid:
        return None
    oauth = OAuth()
    oauth.register(
        name="hf",
        client_id=cid,
        client_secret=os.environ.get("OAUTH_CLIENT_SECRET"),
        server_metadata_url=(
            f"{os.environ.get('OPENID_PROVIDER_URL', 'https://huggingface.co')}"
            "/.well-known/openid-configuration"
        ),
        client_kwargs={"scope": "openid profile"},
    )
    return oauth


# Module-level oauth instance; tests may monkeypatch this.
_oauth: OAuth | None = make_oauth()


def make_auth_router() -> APIRouter:
    router = APIRouter()

    @router.get("/login")
    async def login(request: Request):
        if _oauth is None:
            return JSONResponse(
                {"error": "login_unavailable", "detail": "OAuth not configured"},
                status_code=503,
            )
        redirect_uri = request.url_for("callback")
        return await _oauth.hf.authorize_redirect(request, redirect_uri)

    @router.get("/auth/callback", name="callback")
    async def callback(request: Request):
        if _oauth is None:
            return RedirectResponse("/")
        token = await _oauth.hf.authorize_access_token(request)
        # Prefer userinfo claim embedded in token; fall back to id_token sub.
        userinfo = token.get("userinfo") or {}
        sub = userinfo.get("sub") or token.get("sub", "")
        if sub:
            request.session["uid"] = hash_uid(sub)
            request.session["auth"] = True   # real OAuth sign-in (vs anonymous cookie uid)
        return RedirectResponse("/")

    @router.get("/logout")
    async def logout(request: Request):
        request.session.clear()
        return RedirectResponse("/")

    @router.get("/me")
    async def me(request: Request):
        # anonymous cookie uid is NOT "signed in"; only a real OAuth login sets auth
        return {"signed_in": bool(request.session.get("auth"))}

    return router