use LWP::UserAgent;
use LWP::Debug qw(level);  level('+');

my $url = 'https://www.myurl.com/cgi-bin/file-download';

$ENV{HTTPS_PROXY} = 'PROXY';
$ENV{HTTPS_PROXY_USERNAME} = 'PROXY_USERNAME';
$ENV{HTTPS_PROXY_PASSWORD} = 'PROXY_PASSWORD';

my $ua = LWP::UserAgent->new;
$ua->proxy(['http','https']);

my $response = $ua->post(
	$url, 
	Content_Type => 'form-data',
	Content => [
	userid           => 'USERID',
	password         => 'PASSWORD',
	recordlength     => '',
	recordterminator => 'NONE',
	remotefilename   => 'REMOTE_FILENAME'
	]	);

if ($response->is_success) {
  print $response->content;
} else {
  die $response->status_line;
}