Answered: Https Digest Auth with Json Sample

Digest Authentication is performed automatically, if requested by the server. You only need to set the Credentials property on the WebClient or HttpRequest.

You can test it against httpbin.org like this:

using (var client = new Rebex.Net.WebClient())
{
    client.Credentials = new NetworkCredential("usr", "pwd");
    var authTest = client.DownloadString("http://httpbin.org/digest-auth/auth/usr/pwd");
    Console.WriteLine(authTest);
}

Unfortunately, httpbin.org does not support POST for digest-auth testing. However, it would work the same way, just instead DownloadString use the UploadString method.

If the UploadString method does not work with your server and you get for example 400 Bad Request. response, your server probably requires Content-Type header to be specified. In such case, you cannot use simple WebClient.UploadString() method, but you need to do it using HttpRequst API.

You can test it against reqres.in like this:

var creator = new HttpRequestCreator();

var req = (WebRequest)creator.Create("https://reqres.in/api/login");
req.Method = "POST";
req.Headers.Add("Accept", "application/json");
req.Headers.Add("Content-Type", "application/json");
req.Credentials = new NetworkCredential("eve.holt", "pwd");
using (var upload = new StreamWriter(req.GetRequestStream()))
{
    var data = @"{""email"": ""eve.holt@reqres.in"", ""password"": ""pwd""}";
    upload.Write(data);
}

var res = req.GetResponse();
using (var download = new StreamReader(res.GetResponseStream()))
{
    var response = download.ReadToEnd();
    Console.WriteLine(response);
}