/// <summary>
        /// 发送POST请求
        /// </summary>
        /// <param name="json"></param>
        /// <returns></returns>
        public static string HttpPost(string requestBody)
        {
            string responseMsg = "";
            try
            {

                HttpWebRequest request;
                //设置https验证方式
                if (url.StartsWith("https", StringComparison.OrdinalIgnoreCase))
                {
                    ServicePointManager.ServerCertificateValidationCallback =
                            new RemoteCertificateValidationCallback(CheckValidationResult);
                    ServicePointManager.Expect100Continue = true;
                    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
                    request = WebRequest.Create(url) as HttpWebRequest;
                }
                else
                {
                    request = WebRequest.Create(url) as HttpWebRequest;
                }
                request.ContentType = "application/x-www-form-urlencoded";
                request.Method = "POST";
                request.Timeout = HttpTimeOut;
                request.ReadWriteTimeout = HttpTimeOut;

                byte[] data = Encoding.Default.GetBytes(requestBody);
                using (Stream stream = request.GetRequestStream())
                {
                    stream.Write(data, 0, data.Length);
                }

                StreamReader sr = new StreamReader(request.GetResponse().GetResponseStream());
                responseMsg = sr.ReadToEnd();
            }
            catch (Exception ex)
            {
                LogHelper.WriteLog("HttpPost", ex);
            }
            return responseMsg;
        }