code: func NewAuthorizer(access services.Access, identity services.UserGetter, trust services.Trust) (Authorizer, error) {
  	if access == nil {
  		return nil, trace.BadParameter("missing parameter access")
  	}
  	if identity == nil {
  		return nil, trace.BadParameter("missing parameter identity")
  	}
  	if trust == nil {
  		return nil, trace.BadParameter("missing parameter trust")
  	}
  	return &authorizer{access: access, identity: identity, trust: trust}, nil
  }
docs: // NewAuthorizer returns new authorizer using backends