Ember simple auth authenticateSession - provide session data

I'm trying to pass some session data to authenticateSession using the following:

var session = Ember.Object.extend({
    init() {
        this.set('x-access-token', 'some-access-token');
    }
});

authenticateSession(this.application, session);

However my tests are failing because x-access-token doesn't exist inside my app - how should I be initialising session data for authenticateSession?

I have also tried with:

authenticateSession(this.application, {
    secure:{
        'x-access-token': 'some-access-token'
    }
});