How to use Google API credentials json on Heroku?

Question

I\'m making an app using Google Calendar API, and planning to build it on Heroku.
I have a problem about authentication. Usually I use credential json file for that, but

Answer 1

A more official Heroku documentation in this topic: https://elements.heroku.com/buildpacks/buyersight/heroku-google-application-credentials-buildpack

I also used buyersight's buildpack and it was the only one, which worked for me