Ok, interesting. I tried that myself and I couldn't get it to work either. I then tried subclassing LWP::UserAgent, and overriding the get_basic_credentials method (you should have a program called lwp_request, the source of which should provide an example). I tested my bot with my local cups server, which requires HTTP authentication, and it worked.

code shown below:

#!/usr/bin/perl

use warnings;
use strict;
use LWP::UserAgent;


{
        #Create a new package that subclasses LWP::UserAgent.
        # we do this to allow overriding of the get_basic_credentials(
+) method.
        package RequestAgent;
        our @ISA = qw(LWP::UserAgent);

        # All other subs would come from LWP::UserAgent.

        sub get_basic_credentials
        {
                #we only return the password for one location, so no m
+agic necessary
                return ("user", "password");
        }
}

my $ua = RequestAgent->new();

my $response = $ua->get("http://host:port/location");
die "Error while getting ", $response->request->uri,
" -- ", $response->status_line, "\nAborting"
    unless $response->is_success;

print $response->content, "\n";
[download]

(You'll have to comment out the "use warnings" line again)
I'm not sure why the first version didn't work - perhaps I didn't understand the docs correctly

Update: LTjake got there first.