code: func CurrentIdentity(c context.Context) string {
  	p := getPayload(c)
  	if p == nil {
  		return "gce:anonymous"
  	}
  	// GCE hostnames must be unique per project, so <instance, project> suffices.
  	return fmt.Sprintf("gce:%s:%s", p.Instance, p.Project)
  }
docs: // CurrentIdentity returns the identity of the VM stored in the current context.