PostAsJsonAsync cannot find requested URI

Question

I am currently learning how to create C# server with OWIN and Katana.

I am trying to respond to a POST, but unfortunately it does not find the function.

So this is what I have:

This is a user side class, which is sending user data (username and password) via POST (PostAsJsonAsync()).

public class UserRegisterClient
{
    string _accessToken;
    Uri _baseRequestUri; // http://localhost:8080
    public UserRegisterClient(Uri baseUri, string accessToken)
    {
        _accessToken = accessToken;
        _baseRequestUri = new Uri(baseUri, "api/register/");
    }

    // Handy helper method to set the access token for each request:
    void SetClientAuthentication(HttpClient client)
    {
        client.DefaultRequestHeaders.Authorization
            = new AuthenticationHeaderValue("Bearer", _accessToken);
    }

    public async Task<HttpStatusCode> AddUserAsync(string username, string password)
    {
        HttpResponseMessage response;
        using (var client = new HttpClient())
        {
            SetClientAuthentication(client);
            response = await client.PostAsJsonAsync(
                _baseRequestUri.ToString(), new KeyValuePair<string, string>(username, password));
        }
        return response.StatusCode;
    }
}

Additional information:
in the AddUserAsync function client.PostAsJsonAsync() returns the following:

response =  
{
    StatusCode: 404,
    ReasonPhrase: 'Not Found',
    Version: 1.1,
    Content: System.Net.Http.StreamContent,
    Headers: 
    {   
        Date: Sat, 11 Jul 2015
        18:16:53 GMT   Server: Microsoft-HTTPAPI/2.0   Content-Length: 190  
        Content-Type: application/json; charset=utf-8
    }
}   System.Net.Http.HttpResponseMessage

On the server side, I have a controller, that looks like this:

[RoutePrefix("api/register/")]
class RegisterController : ApiController
{
    public async Task<IHttpActionResult> Post(KeyValuePair<string, string> userData) 
    {
       // I never get inside here
    }
}

On the server side, in the Startup class, you can see the route setup:

private HttpConfiguration ConfigureWebApi()
{
      var config = new HttpConfiguration();
      config.Routes.MapHttpRoute(
           "DefaultApi",
           "api/{controller}/{id}",
           new { id = RouteParameter.Optional });
      return config;
}

Edit: changed Route to RoutePrefix before my controller class.

Answer 1

Make the Controller class public.

[Route("api/register/")]
public class RegisterController : ApiController

Not being public means that the Web API system cannot discover the controller and its actions.