Yes. I cannot see any use case of it.
In my case, I only need to perhaps prevent hotlinking. That is about it.
What exactly the permission system in phpbb is trying to achieve? Trying to restrict the access to a file to certain forum groups so that one link will work for one user and not work for another? I cannot see the reason why anyone would use such a feature, but I explained how it can be implemented via basic auth.
Code execution where? On the server side? It is a job of webserver to decide what can or cannot be executed. And it is a job of system administrator to setup the webserver correctly.
Or do you actually believe that the installation and running of a forum can be done "in a few clicks" by a person who has no clue whatsoever what he is doing?