From lpwcook in perldoc:

Some proxies also require that you send it a username/password in order to let requests through. You should be able to add the required header, with something like this:

 use LWP::UserAgent;
 $ua = LWP::UserAgent->new;
 $ua->proxy(['http', 'ftp'] => 'http://proxy.myorg.com');
 $req = HTTP::Request->new('GET',"http://www.perl.com";);
 $req->proxy_authorization_basic("proxy_user", "proxy_password");
 $res = $ua->request($req);
 print $res->content if $res->is_success;
[download]

Replace proxy.myorg.com, proxy_user and proxy_password with something suitable for your site.

HTH
--
idnopheq
Apply yourself to new problems without preparation, develop confidence in your ability to to meet situations as they arrise.

~ Shunryu Suzuki