code: func CanAccessMaster(c context.Context, name string) error {
  	if ex, err := datastore.Exists(c, &masterPublic{Name: name}); err == nil && ex.Get(0) {
  		// It exists => it is public
  		return nil
  	}
  
  	if isAllowedInternal(c) {
  		return nil
  	}
  
  	code := grpcutil.NotFoundTag
  	if auth.CurrentUser(c).Identity == identity.AnonymousIdentity {
  		code = grpcutil.UnauthenticatedTag
  	}
  	// Act like master does not exist.
  	return errors.Reason("master %q not found", name).Tag(code).Err()
  }
docs: // CanAccessMaster returns nil if the currently logged in user can see the
  // masters, or if the given master is a known public master,
  // otherwise an error.