expose the expires_at property so that apps can setup a timer to try login again before the token expires

[jstrachan]

nice work on this library BTW, its working like a charm!

My only issue is tokens time out after about 24 hours; so rather than the app becoming unresponsive I'd like to setup a timer that if the user leaves their browser open the UI automatically redirects to the login page when the token expires. To do this I just need a public method to expose the expires_at property thats stored in the local / session storage