EDIT

            User user = User.NewInstance(extraUsername, extraPassword);

            userService.createUser(user);

            Group editorGroup = getRemoteApplicationController().getGroupService().find(editorGroupUuid);

            user = userService.load(user.getUuid());

            MergeResult<User> result = userService.merge(user, true);

            user = result.getMergedEntity();

        }