How does the Facebook Like button work?

Question

I want to provide a simple piece of Javascript (or an iframe, I guess) that allows 3rd parties to embed functionality from my site in theirs. The user of said widget will be

Answer 1

Here is a brief explanation of the facebook 'like' button and here is a tutorial on how to build a web widget. Finally here is a discussion on the security of web widgets.

Answer 2

I believe the Like button is using cookies to obtain your FB user information, that with additional attributes are then sent to a service endpoint.

As for security measures, an obvious would be to allow requests only from websites with given access keys.