Remove sso_hint cookie, add sso-clear logout chain

sso_hint on .rose-ash.com was blocked by Safari ITP — the exact
problem we're solving. Replaced with redirect chain: account logout
chains through each client app's /auth/sso-clear to clear all
first-party sessions without any cross-domain cookies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infrastructure/factory.py

@@ -123,40 +123,6 @@ def create_base_app(
         for fn in before_request_fns:
             app.before_request(fn)
 
-    # Silent SSO: if account set sso_hint cookie, trigger OAuth once
-    if name != "account":
-        from urllib.parse import quote as _quote
-
-        @app.before_request
-        async def _sso_check():
-            from quart import session as qs
-            if request.path.startswith("/auth/"):
-                return
-
-            uid = qs.get("uid")
-            has_hint = request.cookies.get("sso_hint")
-
-            # SSO revoked (account logged out) → clear local session
-            if uid and not has_hint:
-                qs.pop("uid", None)
-                qs.pop("cart_sid", None)
-                qs.pop("sso_checked", None)
-                return
-
-            # Already logged in locally
-            if uid:
-                return
-
-            # No hint → nothing to do
-            if not has_hint:
-                return
-
-            # Has hint but no local session → trigger silent OAuth once
-            if qs.get("sso_checked"):
-                return
-            qs["sso_checked"] = True
-            return redirect(f"/auth/login/?next={_quote(request.url, safe='')}")
-
     @app.before_request
     async def _csrf_protect():
         await protect()

infrastructure/oauth.py

@@ -127,16 +127,23 @@ def create_oauth_blueprint(app_name: str) -> Blueprint:
         qsession.clear()
         resp = redirect("/")
         resp.delete_cookie("blog_session", domain=".rose-ash.com", path="/")
-        resp.delete_cookie("sso_hint", domain=".rose-ash.com", path="/")
         return resp
 
+    @bp.get("/sso-clear")
+    @bp.get("/sso-clear/")
+    async def sso_clear():
+        """Clear local session, then redirect to next app in logout chain."""
+        qsession.pop(SESSION_USER_KEY, None)
+        qsession.pop("cart_sid", None)
+        next_url = request.args.get("next", "/")
+        return redirect(next_url)
+
     @bp.post("/logout")
     @bp.post("/logout/")
     async def logout():
         qsession.pop(SESSION_USER_KEY, None)
         qsession.pop("cart_sid", None)
-        qsession.pop("sso_checked", None)
-        # Redirect through account to clear the SSO session too
+        # Redirect through account to clear all app sessions
         return redirect(account_url("/auth/sso-logout/"))
 
     return bp