When calling api routes the Authenticate middleware attempts to redirect you to the login page. If you expect JSON back or don't have auth routes then you don't want this to happen. By re-using the logic from Laravel's exception handler on which format to output we can also determine wether to redirect the user to the login page or give them a JSON error response.
Currently, any unauthorized API requests that pass through the `auth` middleware get a redirect to the login page. Adding the `wantsJson` flag to the conditional corrects this behavior.
