private void Button_Click(object sender, RoutedEventArgs e)
        {
            String login_id = login.Text,
                   pass     = password.Password;

            User user = SecurityClient.validateUser(1, login_id, pass);

            if (user == null)
            {
                MessageBox.Show("Failure");
            }
            else
            {
                password.Password = "";
                new controlPanel(user, this).Show();
            }
        }