code: func (a *authorizer) authorizeBuiltinRole(r BuiltinRole) (*AuthContext, error) {
  	config, err := r.GetClusterConfig()
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return contextForBuiltinRole(r.ClusterName, config, r.Role, r.Username)
  }
docs: // authorizeBuiltinRole authorizes builtin role