項目過程中，由於是收銀系統需要從服務器獲取支付二維碼，會產生SSL連接的問題，在win7、win10上都沒有問題，放到WIN XP上出現了The underlying connection was closed:could not establish trust，

經過查閱相關資料發現是證書問題，采用了最簡單的快捷的禁止證書驗證，代碼如下

//將客戶端訪問的證書修改為無證書
ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true
 
;

代碼放置的位置為進行HTTPwebRequest請求時，完全代碼如下

 /// <summary>
        /// 建立連接
        /// </summary>
        /// <param name="sendmenssage">發送字符串   
        /// <param name="message"></param>
        /// <returns></returns>
        public bool HttpConn(string sendmenssage, out string message)
        {
            
 
try
            {
                //將客戶端訪問的證書修改為無證書
                ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true;


                request = (HttpWebRequest)WebRequest.Create(Common.Const.QueryUrl);//原因是這  每次都是一個新的request  上次abort不影響
                request.Method = "
 
POST";
                request.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; SV1; .NET CLR 2.0.1124)";
                //  request.ContentType = "application/octet-stream";//get
                request.ContentType = "application/x-www-form-urlencoded;";//post
                //   request.Accept = "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
                request.Accept = "*/*";
                request.Timeout = 20 * 1000;
                request.AllowAutoRedirect = true;
                StringBuilder data = new StringBuilder();
                data.Append(sendmenssage);
                //    MyMsgBox.Show("send:" + sendmenssage+"\n "+this.GetHashCode());
                Byte[] bytes = System.Text.Encoding.Default.GetBytes(data.ToString());
                request.ContentLength = bytes.Length;
                //AsyncCallback ac1 = null;
                //ac1 = new AsyncCallback((IAsyncResult r) => { Stream writer = request.EndGetRequestStream(r); writer.Write(bytes, 0, bytes.Length); writer.Close(); });

                //request.BeginGetRequestStream(ac1, null);
                using (Stream writer = request.GetRequestStream())
                {//同樣的請求會卡在這
                    writer.Write(bytes, 0, bytes.Length);
                    writer.Close();
                }
                HttpWebResponse response;
                // 獲得響應流
                using (response = (HttpWebResponse)request.GetResponse())
                {
                    Stream s;
                    s = response.GetResponseStream();
                    StreamReader reader = new StreamReader(s);
                    StringBuilder sb = new StringBuilder();
                    string tmp = reader.ReadLine();
                    while (tmp != null)
                    {
                        sb.Append(tmp);
                        tmp = reader.ReadLine();
                    }
                    reader.Close();
                    message = sb.ToString();
                }
                request.Abort();
                return true;
            }
            catch (Exception e)
            {
                Log.WriteLog("服務器連接異常:" + e.Message);
                message = "";
                return false;
            }
        }

XP環境下的網絡證書問題