Config PHP Intranet To Connect To LDAP DB For VPN

I have an intranet website built for a company, which is hosted on their own VPN. Each user in the company has their own computer at the office which is always logged in to their account via a LDAP directory. Then there is the intranet which is displayed on their browser. What the client wants is a way so that the intranet which is built in PHP can detect whos' computer it is ran on to login then is the intranet as that user. Currently it uses a username and password form to login in a user. So Now I want to compare the unique username of the users computer(LPAD) with my MYSQL table to get the appropriate user. I will have their usernames with be associated with their profile. I pretty much just need someone to update my script to grab the current LPAD username, thats it. Then i can take that to build out the rest of the site