code: func (id *Identity) Subject() pkix.Name {
  	subject := pkix.Name{
  		CommonName: id.Username,
  	}
  	subject.Organization = append([]string{}, id.Groups...)
  	subject.OrganizationalUnit = append([]string{}, id.Usage...)
  	subject.Locality = append([]string{}, id.Principals...)
  	subject.Province = append([]string{}, id.KubernetesGroups...)
  	return subject
  }
docs: // Subject converts identity to X.509 subject name