code: func (s *ClusterConfigurationService) SetAuthPreference(preferences services.AuthPreference) error {
  	value, err := services.GetAuthPreferenceMarshaler().Marshal(preferences)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  
  	item := backend.Item{
  		Key:   backend.Key(authPrefix, preferencePrefix, generalPrefix),
  		Value: value,
  		ID:    preferences.GetResourceID(),
  	}
  
  	_, err = s.Put(context.TODO(), item)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  
  	return nil
  }
docs: // SetAuthPreference sets the cluster authentication preferences
  // on the backend.