Try it like this:
#!/usr/bin/perl -l
use strict;
use warnings;
use HTTP::Headers;
use HTTP::Request;
use LWP::UserAgent;
my $https_proxy;
my $url = 'https://someproxy.com:80';
my $ua = LWP::UserAgent->new(
verify_hostname => 0,
SSL_ca_file => 'cert.dat',
);
$ua->timeout(10);
$ua->agent("");
$ua->proxy( 'https', $https_proxy );
my $h = HTTP::Headers->new();
$h->proxy_authorization_basic( 'user', 'password' );
my $req = HTTP::Request->new( GET => $url );
my $res = $ua->request($req);
print "header ----" . $res->headers_as_string;
print "response ---" . $res->as_string;