Ember: wait for promise in router.willTransition hook

I want to allow some users to enter a route and others dont.

I used simple auth for authentication and it will load the user data with a promise. Th Problem is that willTransition() does not wait until my user is loaded so it will show the index route before I can check if the user have access to it.

So in router.js I have:

willTransition(oldRoute, nextRoute, transition) {
    return this.get('session').authenticate('authenticator:application').then(() => {
      if(this.get('user.isAdmin')) return true
      else alert('not allowed to enter')
    })
}

This is just an example in real I have more like user.isCat and cat are allowed to enter /cats and /cute routes.

I know that I can check user.isAdmin also in beforeModel() of the route but I have many other routes and permission groups, so I want to have a single place in the router to manage that