Does github.com has support for adding virual refs like gilote as discussed in gitolite or gitosis: permission on directory inside of the repository ?
I need to restrict access at directory level inside the repo.
Any clues?
No, at least not as gitolite VREF.
On Github side, there are a post-receive hook or webhooks, but the are after the push.
The only way to really guard a directory within one Github repo is to make/export that directory in its own GitHub repo, and declare it as a submodule in the first repo.