HttpWebRequest 基础连接已关闭：接收时发生错误

            if (url.StartsWith("https", StringComparison.OrdinalIgnoreCase))
            {
                ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
                ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

            }

注：

1、ServicePointManager 在System.Net 命名空间下

2、SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11  需在.net Framework 4.5 版本下才能支持