Automatic authentication using browser's certificate

Hi all, I would like to setup a login authentication based on users' certificates bundled into the customer's browser. I've added a valid SSL Certificate in my browser, signed with a third-party CA, and I would like that the user connected to my website would be automatically authenticated if his cert is OK for me (without typing any password). Have you got any idea ou do you know any framework to develop this in PHP ? Thanks DeMZed PS / Please visit CA-Cert.org for free community (& certificates) around SSL Authentication