#!/usr/bin/perl

use strict;
use WWW::Mechanize;

my $username = 'admin';
my $password = 'secret';
my $url = 'https://admin.testdomain.com';

my $mech = WWW::Mechanize->new;
$mech->get($url);

$mech->set_fields( 
'ctl00$cntPlaceHolder$UsernameTextBox' => $username, 
'ctl00$cntPlaceHolder$PasswordTextBox' => $password 
);

$mech->submit_form();
my $page = $mech->content();
print $page;