private function resolveHeaders(RequestInterface $request)
 {
     $headers = array();
     foreach ($request->getHeaders() as $name => $values) {
         $headers[] = $name . ': ' . implode(", ", $values);
     }
     return $headers;
 }
 private function resolveHeaders(RequestInterface $request)
 {
     $headers = array();
     foreach ($request->getHeaders() as $name => $values) {
         $headers[] = $name . ': ' . implode(", ", $values);
     }
     $this->options[CURLOPT_HTTPHEADER] = $headers;
 }