Managing multiple client FB accounts

I'm doing the WP to FB integration for my clients on my multisite.

So I've been added to the clients FB fanpage as an admin.

When I'm creating the fb app for the CLIENT'S fb page - how do I ensure that their multisite site only posts to THEIR OWN fb page and not any of the other client fb pages I manage?

Same question goes for granting extended permissions.

cheers

Stef