How to verify a users facebook id when making ajax posts to php in facebook app

Question

I am looking for a way to verify a users facebook id when posting user specific data using ajax.

I want to be able to verify that a facebook user id is correct when post

Answer 1

In the end my solution was to grab the users facebook id via the php sdk and creating a hash of it by adding a salt and encoding it with md5. When posting the form I include both the facebook id and the hash. I can then use the same salt value to double check that the facebook idea is correct before using it. This seems to provide enough security for my needs.