Sure, firstly Create the service account Key https://cloud.google.com/iam/docs/keys-create-delete#iam-service-account-keys-create-console then replace it with GOOGLE_APPLICATION_CREDENTIALS_JSON here https://hexdocs.pm/goth/1.3.0-rc.2/Goth.html

Its good practice to encode it in base64 before persisting it in the vault or other Secret management service