Here is my code:
void btnGo_Click(object sender, RoutedEventArgs e)
{
WebClient proxy = new WebClient();
string strUri = "http://10.6.16.163:21829/RestService.svc/IsUserAuthenticated;
proxy.OpenReadCompleted+=new OpenReadCompletedEventHandler(proxy_OpenReadCompleted);
proxy.OpenReadAsync(new Uri(strUri));
}