Authentication

Hi,
We have developped a web portal that is used by hundreds of schools in the province of Quebec. We're looking at the possibility of using Moodle as a complement to our existing portal. What we would like is to be able to redirect an already logged in user from our portal via URL or some other way directly to a course in Moodle.

I have found a way and I'm pretty sure another "cleaner" way of doing this must exist. I have found through these discussion groups (thanks to all who contribute) the file post.php which I have slightly modified. It now looks like this :
<?php
$username = stripslashes($_GET['username']);
$password = stripslashes($_GET['pass']);
$id = stripslashes($_GET['id']);
?>
<form action="http://linux.grics.qc.ca/moodle/login/index.php" method="post" name="login" id="form">
<p><input type="text" name="username" value="<?php echo $username ?>">
<p><input type="hidden" name="password" value="<?php echo $password ?>">
<p><input type="hidden" name="id" value="<?php echo $id ?>">
<script language="JavaScript">
function Validate()
{
document.login.submit();
}
Validate();
</script>
</form>
?>

All I did is to add the notion of "id".
I then hacked the file login/index.php. Around line 168 the "else" now looks like this:
else {
$id=$frm->id;
if ( $id == "" )
{ $id = 01; }
$urltogo = $CFG->wwwroot.'/course/view.php?id='.$id;
unset($SESSION->wantsurl); /// Just in case
}

It works. All I have to do is to send a URL that looks like this :
https://mycompany.qc.ca/moodle/post.php?username=user&pass=password&id=xx
and I get logged in and redirected to the course I wanted.
Now for my questions...
Is there a more proper way to do this? If there is, I would really appreciate someone telling me. I am asking because the fact that I had to "hack" login/index.php means that everytime someone is going to upgrade his/her Moodle, my phone is going to ring... unless it becomes part of Moodle itself.
Thanks in advance.