code: func validateRoles(roles string) error {
  	for _, role := range strings.Split(roles, ",") {
  		switch role {
  		case defaults.RoleAuthService,
  			defaults.RoleNode,
  			defaults.RoleProxy:
  			break
  		default:
  			return trace.Errorf("unknown role: '%s'", role)
  		}
  	}
  	return nil
  }
docs: // validateRoles makes sure that value upassed to --roles flag is valid