public function register($packageName, $appId)
    {
        $this->logger->info(sprintf('Registering application "%s" (%s).', $packageName, $appId));
        $message = json_encode([
            'pkg_name' => (string) $packageName,
            'appid' => (string) $appId,
        ]);

        return $this->publish(self::REG_REQ_TOPIC, $message, self::QOS_LEVEL);
    }