Consuming Web Service with authentication - C#

Question

Good afternoon Personal.

I’m implementing a function in my system to consume data from a web service that requires authentication (Basic Authentication), but I can’t get any feedback. The question is whether the authentication is correct. I searched here on the same site methods to do this and found the following: insert link description here insert link description here

Following these two links I created my method which was as follows:

try
                {
                    var authData = string.Format("{0}:{1}", "Usuario", "Senha");

                    var authHeaderValue = Convert.ToBase64String(Encoding.UTF8.GetBytes(authData));

                    HttpClient cliente = new HttpClient();

                    var uri = new Uri("https://linkdoService");

                    cliente.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authHeaderValue);

                    var json = JsonConvert.SerializeObject(usuario, Formatting.Indented);

                    var content = new StringContent(json, Encoding.UTF8);

                    var resposta = await cliente.PostAsync(uri, content);
                }

The code is not complete, because I stop the execution of the application to check what is returning me and in case the variable reply is always "null". Could someone tell me if this method is correct or am forgetting something to accomplish this request.

Obs1: I am using the Postman program for testing, when using the URL and the authentication keys Postman makes the normal return, that is, send a Json and return a Json as well.

Note: I also tested the Json I am sending to the Web Service, in case the Json created by this line:

var json = JsonConvert.SerializeObject(usuario, Formatting.Indented);

works normally on Postman.

Thanks in advance to anyone who can help, give a hint.