解决基础连接已经关闭: 未能为 SSL/TLS 安全通道建立信任关系

1. 加入命名空间

using System.Net;
using System.Security.Cryptography.X509Certificates;
using System.Net.Security;

2. 再重载CheckValidationResult方法

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

3. 在 new NetworkCredential(userName, password);后加入一行代码

 ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);//验证服务器证书回调自动验证