I'm a fan of WWW::Mechanize. Below is an example. the cookie jar is not always needed of course.

use strict;
use WWW::Mechanize;
use Data::Dumper;
use HTTP::Cookies; 

my $server_name = "https://flutest.lanl.gov";

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

warn "testing on $server_name";

my $results = $mech->get($server_name);
#warn Dumper $results;

if($results->content =~ /please enter your login and password to authenticate/)
  {
    print "site is up";
  }
else
  {
    warn Dumper $results;
    die "site is down!!!";
  }