Add a test for expiry of cached introspection responses

tests/handlers/test_oauth_delegation.py

@@ -539,6 +539,44 @@ class MSC3861OAuthDelegation(HomeserverTestCase):
         error = self.get_failure(self.auth.get_user_by_req(request), SynapseError)
         self.assertEqual(error.value.code, 503)
 
+    def test_cached_expired_introspection(self) -> None:
+        """The handler should raise an error if the introspection response gives
+        an expiry time, the introspection response is cached and then the entry is
+        re-requested after it has expired."""
+
+        self.http_client.request = introspection_mock = AsyncMock(
+            return_value=FakeResponse.json(
+                code=200,
+                payload={
+                    "active": True,
+                    "sub": SUBJECT,
+                    "scope": " ".join(
+                        [
+                            MATRIX_USER_SCOPE,
+                            f"{MATRIX_DEVICE_SCOPE_PREFIX}AABBCC",
+                        ]
+                    ),
+                    "username": USERNAME,
+                    "expires_in": 60,
+                },
+            )
+        )
+        request = Mock(args={})
+        request.args[b"access_token"] = [b"mockAccessToken"]
+        request.requestHeaders.getRawHeaders = mock_getRawHeaders()
+
+        # The first CS-API request causes a successful introspection
+        self.get_success(self.auth.get_user_by_req(request))
+        self.assertEqual(introspection_mock.call_count, 1)
+
+        # Sleep for 60 seconds so the token expires.
+        self.reactor.advance(60.0)
+
+        # Now the CS-API request fails because the token expired
+        self.get_failure(self.auth.get_user_by_req(request), InvalidClientTokenError)
+        # Ensure another introspection request was not sent
+        self.assertEqual(introspection_mock.call_count, 1)
+
     def make_device_keys(self, user_id: str, device_id: str) -> JsonDict:
         # We only generate a master key to simplify the test.
         master_signing_key = generate_signing_key(device_id)