HttpWebRequestreq = (HttpWebRequest)HttpWebRequest.Create(url);

ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
//设置协议类型前设置协议版本
req.ProtocolVersion = HttpVersion.Version11;
//这里设置了协议类型。
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

ServicePointManager.CheckCertificateRevocationList = true;
ServicePointManager.DefaultConnectionLimit = 1000;
ServicePointManager.Expect100Continue = false;