UPDATE (03/10/2022): .NET 6 should now successfully do digest authentication, as kindly pointed by someone in the example repository. Should save you the hassle of doing it manually, like in this repository!

This project contains an extension method in HttpClientExtensions that should work out of the box for basic digest authentication, and be a good starting point to expand upon.

I couldn't personally find a way within .NET to handle digest authentication, and the ways that were documented flat out didn't work.

I might release this as a Nuget package if I get the time.

The integration test in HttpClientExtensionTests provides the best example usage of the simple extension method:

var client = new HttpClient();
client.BaseAddress = new Uri("https://httpbin.org");
var request = new HttpRequestMessage(HttpMethod.Get, "/digest-auth/auth/username/password");
request.Headers.Add("Accept", "*/*");
request.Headers.Add("User-Agent", "HttpClientDigestAuthTester");
request.Headers.Add("Accept-Encoding", "gzip, deflate, br");
request.Headers.Add("Connection", "keep-alive");

var response = await client.SendWithDigestAuthAsync(request, HttpCompletionOption.ResponseContentRead, "username", "password");

The HttpClientDigestAuth targets .NET Core 3.1, as this is most supported, being a LTS release, and stable .NET version before the newly released .NET 6.0.