I have a WordPress site installed in the root folder. Beneath the root is a /docs folder with a bunch of older html files. I'd like to allow only logged in WordPress users to be able to have access to those /docs html pages (not to be confused with WordPress 'pages').

I created a WordPress 'portal' page which displays links to the /docs pages if the visitor is logged in. I would also like to put in a textual search function (which I know how to do) so logged in visitors can get a list of relevant /docs html pages

What I *don't* know how to do is prevent *not* logged in visitors from direct access to the /docs pages for both links and searches?

I know I could do these if I converted the html pages to php and checked a referer. But I don't want to have to redo all the old html if possible (if I have to do *that* I'll just import them into a WordPress taxonomy -- but I hope to avoid that!)

I looked at .htaccess and I was hoping to perhaps set an ENV variable or use REFERER, but I keep reading that such things are not reliable.

Ideas?