v0.2.4

• Support Application Default Credentials as the default authentication mechanism.
  • This still falls back to using the service account if no other credentials are found so there should be no change for existing users.
  • The environment variable GOOGLE_APPLICATION_CREDENTIALS specifies the path to the credentials file; if this is not set or does not contain valid credentials, the default path is $HOME/.config/gcloud/application_default_credentials.json ($HOME usually resolves to /root on GCE).
  • auth_method is now deprecated; we emit a warning if it is configured. private_key is still supported for existing users.
• Support setting custom GCE metadata from config
  • new configuration options fetch_gce_metadata, project_id, zone, vm_id