code: public function post($url, $data = null, $auth = null) {
          $this->setUrl($url);
          $this->setCurlOption(CURLOPT_POST, true);
          if (!is_null($data)) {
              $this->setCurlOption(CURLOPT_POSTFIELDS, http_build_query($data));
          }
  
          if (!is_null($auth)) {
              $this->requireAuth($auth['user'], $auth['password']);
          } else {
              $this->setNoAuth();
          }
  
          return $this->curlExec();
      }
docs: HTTP POST
  @param string $url
  @param array $data post data
  @param array|null $auth [null] array with indexes user and password
  @return string response data(maybe html or json)