Question: I have a website which uses Facebook's registration plugin.

Everything is working fine, I have one issue though: if somebody was on Facebook and unauthorized my application then never returned to my site, how would I know?

The reason I am asking is I am storing user data in a database, namely the `access_token`, Facebook ID and (custom field) username, along with their `joined` date and `last_active` date.

Is there any way that Facebook can interact with my site when a user has unauthorized my app, allowing me to remove them from my site database?

Even something simple like:

```
$unauth_url = 'http://example.com/unauthorize';
file_get_contents($unauth_url . '?signed_request=' . $signed_facebook_request);

```

which runs when the page is app is removed would get the job done.

Is there anything like this available?

Answer: 
There is an interesting option in the fb platform called [Deauthorize Callback](http://developers.facebook.com/docs/authentication) ... It simple calls a page on your app or site when a user removes your app. Simple put the database record deletion code in this page...
In your configuration of your facebook-app there is an option called deauth-request(or similar to that). There you can define a callback url, which will be invoked if somebody unauthorizes your app. Facebook passes soem POST information with that request to recognize the user for example.

You just have to implement a script on your server which deletes the user with that accesstoken from your database.