POST
is just a fancy constructor for a HTTP::Request
object. Use that to construct your request object, and then set authentication:
use HTTP::Request::Common;
my $browser = LWP::UserAgent->new;
my $request = POST $url,
Content => [
Name => $name,
Address => $address,
];
$request->authorization_basic($user, $pass);
my $response = $browser->request($request);