public function downloadFileFromURL($url)
    {
        $request     = new \Google_Http_Request($url, 'GET', null, null);
        $httpRequest = $this->service->getClient()
           ->getAuth()
           ->authenticatedRequest($request);
        if ($httpRequest->getResponseHttpCode() == 200) {
            return $httpRequest->getResponseBody();
        } else {
            // An error occurred.
            return null;
        }
    }