As well as OAuth2 authentication, you can authenticate without user interaction via Service accounts. This involves downloading a secret JSON key with the authentication details.
To use, go to your Project in the https://console.developers.google.com/apis/credentials/serviceaccountkey
and select JSON Key type. Save the file
to your computer and call it via supplying
the file path to the
Navigate to it via: Google Dev Console > Credentials > New credentials > Service account Key > Select service account > Key type = JSON
gar_auth_service(json_file, scope = getOption("googleAuthR.scopes.selected"))
(Invisible) Sets authentication token