index.html

@@ -19,9 +19,8 @@
         </form>
         {% endif %}
         {% else %}
-        <p>The collection mailbox is not connected yet. In a private window: open this page, sign in with
-           <strong>your own account</strong>, click “Connect mailbox”, then sign in as
-           <strong>{{ email_address }}</strong> (technical account).</p>
+        <p>The collection mailbox is not connected yet. Open <code>/connect</code> of this site in a private
+           window and sign in as <strong>{{ email_address }}</strong> (technical account).</p>
         <form action="/connect" method="get">
             <button type="submit" class="btn-primary">Connect mailbox</button>
         </form>

oauth.py

@@ -21,6 +21,7 @@ from cryptography.fernet import Fernet, InvalidToken
 SCOPES = "openid profile email offline_access"
 REFRESH_MARGIN_SEC = 60
 PENDING_TTL_SEC = 600
+MAX_PENDING = 20   # /connect is reachable without login: bound the open requests
 
 
 class OAuthError(Exception):
@@ -108,6 +109,8 @@ class MailboxOAuth:
         now = self.clock()
         with self._lock:
             self._pending = {k: v for k, v in self._pending.items() if now - v[1] < PENDING_TTL_SEC}
+            while len(self._pending) >= MAX_PENDING:
+                del self._pending[min(self._pending, key=lambda k: self._pending[k][1])]
             self._pending[state] = (verifier, now)
         query = {
             "response_type": "code",

tests/test_oauth.py

@@ -166,3 +166,10 @@ def test_callback_error_is_shown(monkeypatch):
     monkeypatch.setattr(unsub, "OAUTH", FakeOAuth())
     r = unsub.app.test_client().get("/oidc/callback?state=s&code=c")
     assert r.status_code == 400 and "expected unsubscribe-bot" in r.get_data(as_text=True)
+
+
+def test_pending_requests_are_bounded(tmp_path):
+    mb = _mb(tmp_path, [])
+    for _ in range(oauth.MAX_PENDING + 15):
+        mb.start()
+    assert len(mb._pending) == oauth.MAX_PENDING