How to EnableTLS 1.2 from ASP.net core 1.1.2 Httpclient

We are using ASP.net core 1.1.2 and we are calling a HTTPS service which is TLS1.2 enabled. When we call from Httpclient we get the following security error.

System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.Http.WinHttpException: A security error occurred 
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) 
   at System.Net.Http.WinHttpHandler.<StartRequest>d__105.MoveNext()

Is there any way to enable TLS1.2 using httpclient using ASP core 1.x

The same https call works fine from postman

Note: We tried many possibilities like below,but none of them worked.

1. handler.ClientCertificateOptions = ClientCertificateOption.Automatic;
   handler.SslProtocols = SslProtocols.Tls11 |  SslProtocols.Tls12 | SslProtocols.Tls;
   handler.PreAuthenticate = true;
   handler.ServerCertificateCustomValidationCallback += (message, cert, chain, errors) => { return true; };
   

2. We tried adding options to registry key, this also failed

The new server has new ciphers added and The client must support one of the following TLS 1.2 cipher suites:

TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384