public function createRegistrationId()
    {
        $registration = new GcmRegistration();
        // build uri
        $uri = $this->endpoint.$this->hubPath.'/registrationIDs/';

        $token = $this->generateSasToken($uri);
        $headers = array_merge(['Authorization: '.$token], $registration->getHeaders());
        $headers = array_merge(['Content-length: 0'], $headers);

        $response = $this->request(self::METHOD_POST, $uri.self::API_VERSION, $headers, null, true);

        preg_match(
            '#'.$uri.'([^?]+)'.preg_quote(self::API_VERSION).'#',
            $response,
            $matches
        );

        return $matches[1];
    }