I save tokens obtained through authorization and use them for post and similar requests. However I need to know when to re-login in case of token expiration.
Does scribe throw any relative exception ? Judging by the sources it doesn't but maybe it throws any other ? Maybe you can suggest a better way ?
Scribe can't tell if a token is expired or not. There's no standard way in OAuth for the provider to inform you that a token was valid and now it isn't.
It's kind of logical that it works that way, tokens have a life span and after that they become rubbish. There's no way of differentiating between a just-expired token and a random string.
The only way you can check is (surprise!) making a request and seeing if it works. Your client can keep some kind of state to check wether the request is getting an unauthorized response with a previously valid token and in that case try to reauthenticate but, sadly, there's no way the provider (or scribe for that matter) can make that easier for you. Sorry.