Sounds like a job for the
Sitecore.Data.DataProviders.FileSystemDataProvider
I haven't used this in a long while, but it essentially allows you to set up a new Sitecore Database (look in Web.config for how the database id="filesystem" is configured).
Once in place, the file system entries (files, directories) would appear to Sitecore as "any regular item" - and could therefore be controlled by Sitecore Security.
You're likely going to need to implement a bespoke extension to the FileSystemDataProvider, as you would need to persist Sitecore data (like for instance the Security Settings).
All in all, sounds like a lot more work than it would probably be worth.
Have you considered WebDAV as an option?