curl 'https://somesite:8800/?library=Algemeen&function=Login&UserName=SomeUser&Password=SomePass'

##</code><code>##

<table><tr><td><b>Result</b></td><td ID="Result">True</td><tr><tr><td><b>ResultMessage</b></td><td ID="ResultMessage"></td><tr><tr><td><b>SessionToken</b></td><td ID="SessionToken">sometoken</td><tr></table>

##</code><code>##

#! /usr/bin/perl -w

use strict;
use HTTP::Request;
use LWP::UserAgent;

my $ua = LWP::UserAgent->new();

my $url = 'https://somesite:8800/';

my $req = HTTP::Request->new(POST => $url);
$req->content_type('application/x-www-form-urlencoded');
$req->content('library=Algemeen&function=Login&UserName=SomeUser&Password=SomePass');

my $res = $ua->request($req);


if ($res->is_success){
  print $res->content;
}else{
  print $res->status_line, "\n";
}