protected function onStateMismatch()
    {
        $this->logger->warning(
            "OAuth2 response state mismatch: provider: {provider} from {addr}",
            array(
                "provider" => get_class($this->provider),
                "addr" => $_SERVER['REMOTE_ADDR']
            )
        );
        $this->session->remove("oauth2state");
        $this->session->addFlash("error", "Invalid OAuth response.");
        $this->picoAuth->redirectToLogin();
    }