protected function getBrokerSessionData(string $brokerSessionId)
    {
        /** This is basic example and you should do something better. */

        $cacheFileName = 'broker_session_' . $brokerSessionId;

        if (!file_exists($cacheFileName)) {
            return null;
        }

        if (time() - 3600 > filemtime($cacheFileName)) {
            unlink($cacheFileName);

            return null;
        }

        echo file_get_contents($cacheFileName);
    }