code: protected function param($params, $param)
      {
          $params = parent::param($params, $param);
  
          /* 签名 */
          ksort($params);
          $param = [];
          foreach ($params as $key => $value) {
              $param[] = "{$key}={$value}";
          }
          $sign          = implode('', $param) . $this->AppSecret;
          $params['sig'] = md5($sign);
  
          return $params;
      }
docs: 合并默认参数和额外参数
  @param array $params  默认参数
  @param array/string $param 额外参数
  @return array: