Support a callback when access token generated from refresh token

[Scorcher]

I am using OAuth2 to make offline request to YouTube API...
When this library refreshes an access_token using refresh_token it would be very useful to call user specified callback to make possibility storing new token somewhere in centralized storage of application.
Now I should check token changes after each exec of my script to reduce refresh.

For example:

$client = new Google_Client();
$client->setOnRefreshTokenCallback(<lambda from my code>);

[dmyers]

What is the purpose of having the package refresh the token? Can we currently detect the change and store it?

[Scorcher]

Yes, you can. You should check token changes after each call to Google API. If changed - store it and use new one next time. If you will use old one (ignoring changes) - the library will update token every time (it is one more request).

See these two sections for detailed understanding: https://developers.google.com/accounts/docs/OAuth2WebServer#offline

[bshaffer]

please see #905

[tmatsuo]

Can we close this now? #905 seems merged.

[tmatsuo]

Closing. Feel free to re open if you think differently

[bshaffer]

Yep! This is available via Google_Client::setTokenCallback.