code: func NewUserAuthorizer(username string, identity services.UserGetter, access services.Access) (Authorizer, error) {
  	authContext, err := contextForLocalUser(username, identity, access)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return &contextAuthorizer{authContext: *authContext}, nil
  }
docs: // NewUserAuthorizer authorizes everyone as predefined local user