calendar.ts

// Create a new GoogleAuth instance with service-account credentials from a json file.
// Note: credential file location must be set in GOOGLE_APPLICATION_CREDENTIALS env variable
const auth = new google.auth.GoogleAuth({
  scopes: ['https://www.googleapis.com/auth/calendar'],
  clientOptions: {
    // Overwrite JWT subject to 'impersonate' calendar user
    subject: 'wilco@headfwd.com'
  }
});

this.calendar = google.calendar({
  version: 'v3',
  auth: await auth.getClient()
});

this.schedule.scheduleIntervalJob('poller', this.POLLING_INTERVAL, () => this.pollCalendarEvents());