437154 X-Cart - login using facebook account & email address

X-cart has an old login mechanism where users have to create a username. If a user doesn't remember their username, I want people to be able to login to see their previous orders and whatnot by using their email address or logging in using their facebook account. I assume facebook authentication will pass the user's email address back to x-cart. As long as the user has the same email address in the x-cart database as they used with facebook they should be able to login - correct me if I'm wrong - I don't know how facebook's API works. Must support 'anonymous' users: when a customer checkouts without supplying a username and password, an anonymous user account is created. x-cart code must be altered to allow anonymous users to login. code and documentation must be included. Instructions for installing this functionality must include: -step by step installation steps to apply to other x-cart sites (this will be tested on a test site and then moved to live). -x-cart files that need to be changed, including code edits (before and after) x-cart is a PHP shopping cart. X-cart experience is extremely helpful. Bonus for including google account authentication