def group_finder(username, request):
    """Returns a list of group identifiers that the user belongs to, or None
    if the user doesn't belong to any groups.
    
    Right now, I don't have any group specific privileges, so just return that
    the user is a member of the 'users' group.
    """
    if username is not None:
        return ['group:users']
    else:
        return None