I'd use WWW::Mechanize.

use strict;
use warnings;

use WWW::Mechanize;

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

$mech->get( "https://adwords.google.com/select/TrafficEstimatorSandbox
+" );

$mech->submit_form
(
    form_number => 0,
    fields      => 
    {
        "login.userid"    => 'mungo',
        "login.password"  => 'lost-and-alone',
    }
);
[download]