Use new Auth API

Website/Data/AuthenticationProvider.cs

@@ -0,0 +1,19 @@
+using System.Net.Http;
+using System.Threading.Tasks;
+using Website.Models;
+
+namespace Website.Data {
+	public class AuthenticationProvider:ApiClient, IAuthenticationProvider {
+		public AuthenticationProvider(HttpClient client) : base(client) {
+		}
+
+		public async Task<User> Authenticate(LoginRequest request) {
+			try {
+				return await Post<User>("authenticate", request);
+			}
+			catch (ApiCallException) {
+				return null;
+			}
+		}
+	}
+}