请求被中止: 未能创建 SSL/TLS 安全通道

在发送请求前加：

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
ServicePointManager.ServerCertificateValidationCallback=new System.Net.Security.RemoteCertificateValidationCallback(CheckValidationResult);

   public static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {
            return true;
        }