private function _setHeaders($method, $url, $body = NULL)
 {
     if ($method != HttpRequest::GET) {
         $cType = 'application/json';
     } else {
         $cType = NULL;
     }
     $macToken = $this->_mac->MACToken($method, $url, $cType, $body);
     $ua = Utils::getUserAgent(Config::SDK_USER_AGENT, Config::SDK_VERSION);
     return array('Content-Type' => $cType, 'User-Agent' => $ua, 'Authorization' => $macToken);
 }