private static function getOpenIDConfig($key)
 {
     $openIDConfigJSON = SessionCache::get(self::$OPENID_CONFIG_CACHE_KEY);
     if ($openIDConfigJSON == FALSE) {
         $openIDConfigJSON = HttpUtil::processRequest(self::OPENID_CONFIG_URL_KEY);
         SessionCache::set(self::$OPENID_CONFIG_CACHE_KEY, $openIDConfigJSON);
     }
     $openIDConfig = json_decode($openIDConfigJSON, TRUE);
     return $openIDConfig[$key];
 }
 private static function verifySignatureAtGoogle($jwt)
 {
     $response = HttpUtil::processRequest('https://www.googleapis.com/oauth2/v1/tokeninfo', array('id_token' => $jwt));
     return json_decode($response, TRUE);
 }