use Tk;
use Tk::DialogBox;
use strict;
use warnings;

my $mw = MainWindow->new(title => "Password Demo");

my $login_first_try = 1;	
my $id;
my $passwd;

while (1) {
	my $dialog = $mw->DialogBox(-buttons => ["OK", "Cancel"], -title => "Login");
	my $instruction;
	if ($login_first_try) {
		$instruction = "Please provide id/passwd: ";
		$login_first_try = 0;
	} else {
		$instruction = "Failed to login, please try again: "
	}

	$dialog->add("Label", anchor => "w", text => $instruction)->pack(fill => "x");
	my $id_text = $dialog->add("Entry", width => 30)->pack();
	my $passwd_text = $dialog->add("Entry", show => "*", width => 30)->pack();
	$id_text->focus();
	if ($dialog->Show() eq "OK") {
		print "OK pressed, validate here, if okay last and quit the while loop"
		#.............
	} else {
		exit;
	}
}