Setting Heroku Config Var with contents from Google Cloud Service Account Keyfile

Environment variables on heroku, or anywhere, are strings.

If that google api constructor takes a JSON object you may need to do something like this to convert it back to JSON:

const gcs = require('@google-cloud/storage')({
  projectId: 'my-project-ID',
  credentials: JSON.parse(process.env.GCS_KEYFILE)
});