public override void RequestAuthentication(Action <object> completionCallback, object userState)
{
LoginRegistrationWindow window = new LoginRegistrationWindow();
window.Show();
window.Closed += (sender, e) => completionCallback(userState);
}
private void LoginButton_Click(object sender, RoutedEventArgs e)
{
LoginRegistrationWindow loginWindow = new LoginRegistrationWindow();
loginWindow.Show();
}