c# - Make Https call using HttpClient

Question

I have been using HttpClient for making WebApi calls using C#. Seems neat & fast way compared to WebClient. However I am stuck up while making Https calls.

How can I make below code to make Https calls?

HttpClient httpClient = new HttpClient();
httpClient.BaseAddress = new Uri("https://foobar.com/");
httpClient.DefaultRequestHeaders.Accept.Clear();
httpClient.DefaultRequestHeaders.Accept.Add(
                new MediaTypeWithQualityHeaderValue("application/xml"));

var task = httpClient.PostAsXmlAsync<DeviceRequest>(
                "api/SaveData", request);

EDIT 1: The code above works fine for making http calls. But when I change the scheme to https it does not work. Here is the error obtained:

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

EDIT 2: Changing the scheme to https is: step one.

How do I supply certificate & public / private key along with C# request.

Answer 1

If the server only supports higher TLS version like TLS 1.2 only, it will still fail unless your client PC is configured to use higher TLS version by default. To overcome this problem, add the following in your code:

System.Net.ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

Modifying your code example, it would be

HttpClient httpClient = new HttpClient();   

//specify to use TLS 1.2 as default connection
System.Net.ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

httpClient.BaseAddress = new Uri("https://foobar.com/");
httpClient.DefaultRequestHeaders.Accept.Clear();
httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/xml"));
    
var task = httpClient.PostAsXmlAsync<DeviceRequest>("api/SaveData", request);