code: protected function getSign($data)
      {
          if (is_null($this->userConfig->get('mch_key'))) {
              throw new InvalidArgumentException('Missing Config -- [mch_key]');
          }
          ksort($data);
          $string = md5($this->getSignContent($data) . '&key=' . $this->userConfig->get('mch_key'));
          return strtoupper($string);
      }
docs: 生成内容签名
  @param $data
  @return string