Testing in ember-cli with third-party authentication on a PHP backend

I have an app that uses ember-simple-auth for Google authentication. All requests to my PHP backend are authorized with a Google access token, which the backend checks with Google before doing anything else. I understand ember-simple-auth has a testing package, but how would I go about testing this app?

The backend is a part of the app's repository, under app/api/.

An approach would be to customise the PHP code depending on the environment (importing config/environment.js), but it's on the backend and it's written in PHP.