Check if user authorized your application on ios

I'm using the facebook ios Sdk to connect my application with facebook. The login function

[facebook authorize:permissions delegate:self];

calls the delegate

- (void)fbDidLogin

on success, but I would like to know when it was the first time the user authorized the application.

This is to report an achievement on Game Center when the user authorize the application on facebook fo开发者_如何学编程r the first time.

The Graph API doesn't tell you if this was the first time or have any similar date information. You track this on the phones keychain or you could keep track of the user history on your own server.