MainClass.cs

using System;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

namespace Test
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			Console.WriteLine ("Hello World!");
			MainClass m = new MainClass ();
			m.CreateSession ();

			Console.ReadLine ();
		}

		public async Task CreateSession ()
		{
			using (var client = new HttpClient ()) {
				var url = string.Format ("https://localhost/AuthService.svc/" + "ValidateUserNW");

				var json = "{\"Username\":\"jh\",\"Password\":\"kj\"}";

				HttpContent content = new StringContent (json,
					                      Encoding.UTF8,
					                      "application/json");

				try {
					client.DefaultRequestHeaders.Add ("User-Agent", "Finder/1.0.0.0 (Android; Nexus 4 (KitKat) OS 4.4.2)");
				} catch (Exception e) {
					Console.WriteLine (e);
				}


				// Need by service, don't remove
				var resp = await client.PostAsync (url, content);
				Console.WriteLine (resp);
			}
		}
	}
}