docs: def UpdateUser(username, password=None, is_admin=False):
    """Updates the password or privilege-level for a user."""
    user_type, password = _GetUserTypeAndPassword(
        username, password=password, is_admin=is_admin)
    grr_api = maintenance_utils.InitGRRRootAPI()
    grr_user = grr_api.GrrUser(username).Get()
    grr_user.Modify(user_type=user_type, password=password)