Connection NAV 2017 Web Service (Codeunit) with Universal Windows App

Hi,
I hope someone can help me out. I'm just interested in trying out the new Windows Template Studio from VS2017. (btw. it's great)
I Created an app with Navigation Pane and MVVM Light + Grid. Nothing special so far.

In NAV I have a Codeunit Web Service with two parameters. (Request, Response) where Response is by Reference (VAR). I just write Response:= "Hello World" in the Function.

I'm strictly not able to get any result back with my app. I don't post any code here because my code is rubbish. I tried many ways.

In a simple Windows Forms application, I can connect through System.Web.Service

Like this ... Where ProcessRequest is my Function in the Codeunit and Webserv is the Published Service name

using System;
using System.Net;
using System.Web.Services;
using System.Web.Services.Description;
using System.Web.Services.Protocols;
using System.Windows.Forms;

namespace WebserviceTest
{
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [WebServiceBinding(Name = "Webserv_Binding", Namespace = "urn:microsoft-dynamics-schemas/codeunit/Webserv")]
    public class NAV2017ServiceClient : SoapHttpClientProtocol
    {
        public NAV2017ServiceClient(string url, string userName, string password, string domain, int timeout)
        {
            this.Url = url;
            this.Timeout = timeout * 1000;
            if (string.IsNullOrEmpty(userName))
                this.UseDefaultCredentials = true;
            else
                this.Credentials = (ICredentials)new NetworkCredential(userName, password, domain);
        }


        [SoapDocumentMethod("urn:microsoft-dynamics-schemas/codeunit/Webserv:ProcessRequest", ParameterStyle = SoapParameterStyle.Wrapped, RequestNamespace = "urn:microsoft-dynamics-schemas/codeunit/Webserv", ResponseElementName = "ProcessRequest_Result", ResponseNamespace = "urn:microsoft-dynamics-schemas/codeunit/Webserv", Use = SoapBindingUse.Literal)]
        public void ProcessRequest(string request, ref string response)
        {
      
            //MessageBox.Show(this.Url.ToString());            
            object[] objArray = this.Invoke("ProcessRequest", new object[2]
            {
                (object) request,
                (object) response
            });
            
            response = (string)objArray[0];


        }

        protected override WebRequest GetWebRequest(Uri uri)
        {
            WebRequest rq = base.GetWebRequest(uri);            
            return rq;
        }

    }
}

worked like charm . But now I do not have a clue how I could connect to NAV and get my simple response back.

If anyone has some time left and knowledge in this I would love to get an answer how I can achieve this.

It's nothing I'm working on for a customer so there is no need to hurry for me. It's just a "would love to know" thing.

greetings