ServicePointManager.Expect100Continue = true;
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
System.Net.ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);
//证书文件路径
string filePath = "client.p12";
X509Certificate2 cert = new System.Security.Cryptography.X509Certificates.X509Certificate2(filePath, "123456");
this.ClientCertificates.Add(cert);