Get user to pre-authorise app when creating account with google

I am creating an artificial intelligence powered wall display with a UI similar to dakboard, using JS i would like to be able to get the upcoming events on a users calendar and display them, i have found this example which shows the basics of getting a users event but requires the user to sign in on the device, as the device is going to be connecting to a central server to get user config, weather, ect i was hoping there was some way i can pre-generate a key in the phone app (during sign up the user could sign in with their google account and click authorise) so that the user can authorise the calendar app in the app and then after the device is setup it just gets the details from the central server.