https://cloud.google.com/docs/authentication/
https://cloud.google.com/container-registry/docs/advanced-authentication

ADC - application default credentials
https://developers.google.com/identity/protocols/application-default-credentials
https://developers.google.com/accounts/docs/application-default-credentials

https://cloud.google.com/sdk/auth_success

credentials
https://support.google.com/googleapi/answer/6158857
oauth2:
https://support.google.com/googleapi/answer/6158849

gcloud

auth
    application-default print-access-token 
    configure-docker
        $HOME/.docker/config.json