how to intercept the event when a user authorizes my app?

Hello all,
I have developed a facebook app using drupal and dff and i was requested by my client to publish to the wall when a user uses the app for the first time.

i know how to publish in general but i am having some difficulties in finding out where i am suppose to intercept this particular event.

pls help.

hook_fb()

First, read on drupal.org how to implement a custom module. Understand Drupal's hooks.

Modules/fb introduces hook_fb().

Your hook_fb() will be invoked when a user authorizes or revokes authorization. Look for $op == FB_APP_OP_EVENT. And look for $data['event_type'] == FB_APP_EVENT_POST_AUTHORIZE or $data['event_type'] == FB_APP_EVENT_POST_REMOVE.