using RestSharp using HTTPClient using WebClient

callWebAPI.cs

using RestSharp; 
using System.Net;
using System.Net.Http;
        
public static void useRestSharp(string url)
{
    var client = new RestClient(url);
    var request = new RestRequest(Method.POST);

    request.AddHeader("Content-Type", "application/json");
    request.AddParameter("undefined", APIRequest(), ParameterType.RequestBody);
    
    IRestResponse response = client.Execute(request);
    Console.WriteLine(response.Content);
}

public static async void useHTTPClient(string url)
{
    var httpClient = new HttpClient();

    var request = httpClient.PostAsync(url, new StringContent(APIRequest(), Encoding.UTF8, "application/json")).Result;

    var content = await request.Content.ReadAsStringAsync();

    Console.WriteLine(content);
}

public static void useWebClient(string url)
{
    var webClient = new WebClient();

    webClient.Headers[HttpRequestHeader.ContentType] = "application/json";
    var response = webClient.UploadString(url, APIRequest());

    Console.WriteLine(response);
}

// Could be serialized JSON object using json.net or newtonsoft.json
public static string APIRequest()
{
    string source = @"C:\Users\vpetkovic\Desktop\NH example.txt";

    dynamic obj = new ExpandoObject();
    obj.username = "data";
    obj.password = "data";
    obj.fileName = Path.GetFileName(source);
    obj.file = Convert.ToBase64String(File.ReadAllBytes(source));

    string apiRequest = "{\r\n  \"username\": \"" + obj.username + "\",\r\n  \"password\": \"" + obj.password + "\",\r\n  \"fileName\": \"" + obj.fileName + "\",\r\n  \"file\": \"" + obj.file + "\"\r\n}";

    return apiRequest;
}

Hi there! Sorry for late reply.

I am not using Auth0 but based on their documentation found here, you can see how to get token based on the authorization flow you are using. You can see what each flow returns as a response, and in a context of your example above response would be stored in
Content: System.Net.Http.HttpConnectionResponseContent

Now you want to deserialize that json response. To achieve that you can use any json (de)serializer but I think using using HttpClient extensions methods in this sense would be the simplest.
You can install it using package manager console Install-Package System.Net.Http.Json and reference it in using statement. Then you will need to replace line 23 with

var response = await request.Content.ReadFromJsonAsync<TokenResponse>();

where TokenResponse is your expected response object

  public class TokenResponse
  {
      // Other properties removed for brevity
      public string access_token { get; set; }
  }

To further simplify future requests you can install IdentityModel package Install-Package IdentityModel and then store retrieved access token like so:

httpClient.SetBearerToken(response.access_token);

---

Note that this gist is an example for using clients in very short lived console applications hence the class is static, for simplest and quickest of testing. Otherwise, if your use case is different then I suggest you to use IHttpClientFactory to implement resilient HTTP requests

Hey! thanks a lot, you helped me too much! Hugs from Chile

Glad I could help 🙂