auth.js

//app/sessions/application
import Session from 'simple-auth/session';
import Ember from 'ember';
const { computed } = Ember;
const { service } = Ember.inject;

export default Session.extend({
  store: service(),
  user: computed('secure.userId', function(){
    return this.get('store').findRecord('user', this.get('secure.userId'));
  })
});

//config/environment.js
'simple-auth': {
  session: 'session:application'
}

Its not, it should work with 1.13.x.
I am wondering if problem is with store: service(), or with session itself.
If error persists when you comment out this then there must be wrong something like file name, or configuration. Also check that your session is in app/sessions/application.js

//config/environment.js
module.exports = function (environment) {
  var ENV = {
    'simple-auth': {
      session: 'session:application',
    }
  }
}