解决“未能创建 SSL/TLS 安全通道”异常
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3
| SecurityProtocolType.Tls
| SecurityProtocolType.Tls11
| SecurityProtocolType.Tls12;
net4.0环境则加
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3
| SecurityProtocolType.Tls
| (SecurityProtocolType)0x300 //Tls11
| (SecurityProtocolType)0xC00; //Tls12