docs: def get_appapi_params(self, prepay_id, timestamp=None, nonce_str=None):
          """
          获取 APP 支付参数
  
          :param prepay_id: 统一下单接口返回的 prepay_id 参数值
          :param timestamp: 可选，时间戳，默认为当前时间戳
          :param nonce_str: 可选，随机字符串，默认自动生成
          :return: 签名
          """
          data = {
              'appid': self.appid,
              'partnerid': self.mch_id,
              'prepayid': prepay_id,
              'package': 'Sign=WXPay',
              'timestamp': timestamp or to_text(int(time.time())),
              'noncestr': nonce_str or random_string(32)
          }
          sign = calculate_signature(data, self._client.api_key)
          data['sign'] = sign
          return data