eZ\Publish\Core\REST\Client\HttpClient::request PHP Method

    public function request($method, $path, Message $message = null);

 /**
  * Execute a HTTP request to the remote server
  *
  * Returns the result from the remote server. The client sets the correct
  * headers for Basic Auth into the $message transmitted to the inner
  * client.
  *
  * @param string $method
  * @param string $path
  * @param \eZ\Publish\Core\REST\Common\Message $message
  *
  * @return \eZ\Publish\Core\REST\Common\Message
  */
 public function request($method, $path, Message $message = null)
 {
     if ($message === null) {
         $message = new Message();
     }
     $message->headers['Authorization'] = sprintf('Basic %s', base64_encode(sprintf('%s:%s', $this->username, $this->password)));
     return $this->innerClient->request($method, $path, $message);
 }