ESA - Can I use index route as login route

When using Ember Simple Auth add-on, can I use index route to override its login route to be able to redirect to another external login page ? Meaning that, I defined application.js routes as follows:

import { inject as service } from '@ember/service';
import Route from '@ember/routing/route';
import ApplicationRouteMixin from 'ember-simple-auth/mixins/application-route-mixin';

export default Route.extend(ApplicationRouteMixin, {
  currentUser: service('current-user'),
  authenticationRoute: 'index',
  routeAfterAuthentication: 'dashboard',

  beforeModel() {
    return this._loadCurrentUser();

  sessionAuthenticated() {

  _loadCurrentUser() {
    return this.get('currentUser').loadCurrentUser().catch(() => this.get('session').invalidate());

And the index.js route like this:

import Route from '@ember/routing/route';
import { inject as service } from '@ember/service';
import config from '../config/environment';
import isFastBoot from 'ember-simple-auth/utils/is-fastboot';

export default Route.extend({
  session: service('session'),
   _isFastBoot: isFastBoot(),

  beforeModel: function() {
    if (this.get('session.isAuthenticated')) {
    } else {
      if (!this.get('_isFastBoot')) {
        let oauthUrl = config.oauthUrl;
        let clientId = config.clientID;
        let redirectURI = `${window.location.origin}/callback`;
        let responseType = `token`;
        let scope = `profile%20openid`;
                              + `?client_id=${clientId}`
                              + `&redirect_uri=${redirectURI}`
                              + `&response_type=${responseType}`
                              + `&scope=${scope}`

But it does not work.