How to subclass an Ember class using ES6 syntax in Ember CLI

I'd like to create a custom Route class in Ember CLI. I have the following example working in an older app written with globals:

App.AuthenticatedRoute = Ember.Route.Extend({ 
  beforeModel: function() { 
    //Do some things
  }
});

App.DashboardRoute = App.AuthenticatedRoute.Extend({});

I'm familiar enough with ES6 modules to know that the example would look something like this...

var AuthenticatedRoute = Ember.Route.Extend({
  beforeModel: function() { 
    //
  }
});

export default AuthenticatedRoute;

...but I'm curious about the following:

1. Where would this live in the app structure?


2. How do I access this subclass in other modules?