Something like this:

use strict;
use warnings;
use WWW::Mechanize;
my $mech = WWW::Mechanize->new;
$mech->credentials('user', 'pass');
my $response = $mech->get('http://foo.com');

die $response->status_line unless $response->is_success;

printf "content-type: %s\n", $response->header('Content-Type');

my $data = $response->content;
[download]

In response to your update:
You will need Crypt::SSLeay for https traffic. See the section on PKCS12 support.

Updated example:

use strict;
use warnings;
use WWW::Mechanize;
use Crypt::SSLeay;

$ENV{HTTPS_PKCS12_FILE}     = 'certs/pkcs12.pkcs12';
$ENV{HTTPS_PKCS12_PASSWORD} = 'PKCS12_PASSWORD';

my $mech = WWW::Mechanize->new;
$mech->credentials('user', 'pass');
my $response = $mech->get('https://foo.com');

die $response->status_line unless $response->is_success;

printf "content-type: %s\n", $response->header('Content-Type');

my $data = $response->content;
[download]

You might also like to use the search box on the top page or Super Search to find previous discussions about this, such as Secure Site Login with Mechanize.

• Net::SCP
• Net::SFTP

#!/usr/bin/perl -w
#adapted from lwpcook
use strict;
use LWP::UserAgent;

my $user = 'zentara';
my $pass = 'foobar';

my $ua = LWP::UserAgent->new;

my $URL = 'https://zentara.zentara.net/~zentara/zentara1.avi';
my $filename = substr( $URL, rindex( $URL, "/" ) + 1 );
#print "$filename\n";
open( IN, ">$filename" ) or die $!;

print "Fetching $URL\n";

my $expected_length;
my $bytes_received = 0;

my $req = HTTP::Request->new(GET => $URL);
$req->authorization_basic($user, $pass);

my $res = $ua->request($req,
    sub {
        my ( $chunk, $res ) = @_;
        $bytes_received += length($chunk);
        unless ( defined $expected_length ) {
            $expected_length = $res->content_length || 0;
        }
        if ($expected_length) {
            printf STDERR "%d%% - ", 100 * $bytes_received / $expected
+_length;
        }
        print STDERR "$bytes_received bytes received\n";

        # XXX Should really do something with the chunk itself
        print IN $chunk;
    }
);

print $res->status_line, "\n";
close IN;
exit;
[download]

Thank you, very interesting piece :) It even owes a post of its own in the Code Catacombs!