code: func (m *Manager) FilterUsersWithAuthorizations(usernames []string, organization string) ([]string, error) {
  	var auths []Authorization
  	err := m.getAuthorizationCollection().Find(bson.M{"username": bson.M{"$in": usernames}, "grantedto": organization}).Select(bson.M{"username": 1}).All(&auths)
  	if err != nil {
  		return nil, err
  	}
  	result := []string{}
  	for _, auth := range auths {
  		result = append(result, auth.Username)
  	}
  	return result, nil
  }
docs: // FilterUsersWithAuthorizations returns the authorizations granted to an organization