php – Where to find the Facebook cookie? – Stack Overflow

The cookie which Facebook sets that allows your site to access a user’s information (once they’ve agreed to give your “application” access) uses a combination of your application’s ID and “secret” (a long alphanumeric string that you must not share, or other applications would be able to impersonate yours) to set an encrypted value with the user’s ID and an authentication token unique to the user and your application (representing the permission they’ve given you to their data).

https://stackoverflow.com/questions/4763197/where-to-find-the-facebook-cookie