public static function getAuthSubSessionToken(
            $token, $client = null,
            $request_uri = self::AUTHSUB_SESSION_TOKEN_URI)
    {
        $client = self::getHttpClient($token, $client);

        if ($client instanceof Zend_Gdata_HttpClient) {
            $filterResult = $client->filterHttpRequest('GET', $request_uri);
            $url = $filterResult['url'];
            $headers = $filterResult['headers'];
            $client->setHeaders($headers);
            $client->setUri($url);
        } else {
            $client->setUri($request_uri);
        }

        try {
            $response = $client->request('GET');
        } catch (Zend_Http_Client_Exception $e) {
            require_once 'Zend/Gdata/App/HttpException.php';
            throw new Zend_Gdata_App_HttpException($e->getMessage(), $e);
        }

        // Parse Google's response
        if ($response->isSuccessful()) {
            $goog_resp = array();
            foreach (explode("\n", $response->getBody()) as $l) {
                $l = chop($l);
                if ($l) {
                    list($key, $val) = explode('=', chop($l), 2);
                    $goog_resp[$key] = $val;
                }
            }
            return $goog_resp['Token'];
        } else {
            require_once 'Zend/Gdata/App/AuthException.php';
            throw new Zend_Gdata_App_AuthException(
                    'Token upgrade failed. Reason: ' . $response->getBody());
        }
    }