asp.net core 支付宝 电脑2.0支付

public class AlipayConfig
    {
        // 应用ID,您的APPID
        public string app_id = "";

        // 支付宝网关
        public string gatewayUrl = "https://openapi.alipay.com/gateway.do";

        // 商户私钥，您的原始格式RSA私钥
        public string private_key = "";

        // 支付宝公钥,查看地址：https://openhome.alipay.com/platform/keyManage.htm 对应APPID下的支付宝公钥，注意不是应用公钥，不是应用公钥，不是应用公钥。
        public string alipay_public_key = "";

        // 签名方式
        public string sign_type = "RSA2";

        // 编码格式
        public string charset = "UTF-8";

        // 同步回调地址
        public string return_url = ";

        // 异步回调地址
        public string notify_url = "";
    }

public class AlipayService
    {
        #region 字段
        AlipayConfig alipayConfig = new AlipayConfig();

        #endregion

        #region 构造方法
        public AlipayService()
        {

        }
        public AlipayService(AlipayConfig alipayConfig)
        {
            this.alipayConfig = alipayConfig;
        } 
        #endregion

        /// <summary>
        /// 支付宝电脑网站2.0支付，成功返回表单信息直接写入Response,失败返回空
        /// </summary>
        /// <param name="out_trade_no">订单号</param>
        /// <param name="subject">订单名称</param>
        /// <param name="total_amout">付款金额</param>
        /// <param name="body">商品描述</param>
        /// <returns></returns>
        public string GetAliPayTradePayRes(string out_trade_no, string subject, string total_amout, string body)
        {
            DefaultAopClient client = new DefaultAopClient(alipayConfig.gatewayUrl, alipayConfig.app_id, alipayConfig.private_key, "json", "1.0", alipayConfig.sign_type, alipayConfig.alipay_public_key, alipayConfig.charset, false);

            // 组装业务参数model
            AlipayTradePagePayModel model = new AlipayTradePagePayModel();
            model.Body = body;
            model.Subject = subject;
            model.TotalAmount = total_amout;
            model.OutTradeNo = out_trade_no;
            model.ProductCode = "FAST_INSTANT_TRADE_PAY";

            AlipayTradePagePayRequest request = new AlipayTradePagePayRequest();
            // 设置同步回调地址
            request.SetReturnUrl(alipayConfig.return_url);
            // 设置异步通知接收地址
            request.SetNotifyUrl(alipayConfig.notify_url);
            // 将业务model载入到request
            request.SetBizModel(model);

            AlipayTradePagePayResponse response = null;
            try
            {
                response = client.pageExecute(request, null, "post");
                //返回正常生成的表单信息，自动提交到支付宝页面，原生成信息可见改为隐藏
                return response.Body.Replace("<form", "<form style=‘display:none‘");
            }
            catch (Exception exp)
            {
                return "";
            }
        } 
    }