HttpUrl requestUrl = mockWebServer.url(request.getPath());
    String code = requestUrl.queryParameter("code");
    String stateString = requestUrl.queryParameter("state");
    ByteString state = stateString != null ? ByteString.decodeBase64(stateString) : null;

    Listener listener;
    synchronized (this) {
      listener = listeners.get(state);
    }

    if (code == null || listener == null) {