The requested security protocol is not supported

.Net Core访问https接口报错：The requested security protocol is not supported

HttpWebRequestreq = (HttpWebRequest)HttpWebRequest.Create(url);
ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
//设置协议类型前设置协议版本
req.ProtocolVersion = HttpVersion.Version11;
//这里设置了协议类型。
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
ServicePointManager.CheckCertificateRevocationList = true;
ServicePointManager.DefaultConnectionLimit = 1000;
ServicePointManager.Expect100Continue = false;

The SSL connection could not be established, see inner exception

dotnet core在Linux(如：centOS)环境下使用HttpClient请求https可能会报异常：
One or more errors occurred. (The SSL connection could not be established, see inner exception.)
设置如下环境变量暂时解决：

export DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER=0

使用本地https证书

参考文章
.NetCore项目使用Https证书
.net core 配置安全证书及访问Https接口
asp.net core 2使用本地https证书