use LWP::UserAgent;
my $user = "user";
my $pass = "pass";
my $browser = LWP::UserAgent->new();
my $responde = HTTP::Request->new(POST => "http://www.sito.com/index.php");
$responde->content_type("application/x-www-form-urlencoded");
$responde->content("user=" . $user . "&pass=" . $pass);
$browser->request($responde)->as_string