SSO ASPX to PHP with Session Form

#Using Moodle 2.4

I have an aspx (.Net 4) page that authenticates the user.  I have a link that sends the user to the Moodle web server.  On the Moodle server I can get the form session for username, firstname, lastname, etc.  I am not using cookies.

From what I can tell, all I would need to do is override the $username with the form session USERNAME.. 

How do I override the function loginpage_hook() in \lib\authlib.php?

How do I pull form session from aspx?