Bypass auth screen if we already have a token

[jbrooksuk]

Unless the token has expired, the consumer has explicitly requested re-auth or the scopes have changed, we shouldn't need to continue showing the auth screen.

[marcoscoelho]

Same question..

[georgecoca]

@taylorotwell can you take a look at this issue ? This seems problematic when an app it's depending only on oAuth server to authenticate users. And it's annoying to ask each time the user to authorize (even if previously has approved the request).