Getting past Proxy server

I am using the LPW::USERAGENT module to grab a website and obtain 
information.  The Program i have created works without a proxy server but I 
want it to work behind a proxy server where you have to enter a passwd and 
username to get out to the real world websites.
my $ua = LWP::UserAgent->new;
$ua->proxy(['http', 'ftp'], 'http://proxyserver name and port/');

$url= 'http://www.perl.com';

$request = HTTP::Request->new('GET',$url);

It works when it is not behind a proxy but when i had the $ua->proxy part, i 
get an authentication required response msg.  i think i might need to enter 
a user and passwd.  what would be the syntax to do that.
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