code: func MarshalCertRoles(roles []string) (string, error) {
  	out, err := json.Marshal(CertRoles{Version: V1, Roles: roles})
  	if err != nil {
  		return "", trace.Wrap(err)
  	}
  	return string(out), err
  }
docs: // MarshalCertRoles marshal roles list to OpenSSH