User u = service.findOne(id);
if (u != null) {
    // user can only delete their own account
    User authenticated = authenticationFacade.getAuthUser();
    RestPreconditions.checkRequestState(authenticated.getId() == u.getId());
}

Post p = service.findOne(id);
if (p != null) {
        // user can only delete their own posts
        User authenticated = authenticationFacade.getAuthUser();
        RestPreconditions.checkRequestState(authenticated.getId() == p.getUser().getId());
}