code: protected function retData(array $ret)
      {
          $back = new BackAppChargeData($this->config, $ret);
  
          $back->setSign();
          $backData = $back->getData();
  
          return $backData;
      }
docs: 处理APP支付的返回值。直接返回与微信文档对应的字段
  @param array $ret
  
  @return array $data
  
  ```php
  $data = [
  'appid' => '',   // 应用ID
  'partnerid' => '',   // 商户号
  'prepayid'  => '',   // 预支付交易会话ID
  'package'   => '',  // 扩展字段  固定值：Sign=WXPay
  'noncestr'  => '',   // 随机字符串
  'timestamp' => '',   // 时间戳
  'sign'  => '',  // 签名
  ];
  ```
  @author helei