HTML Document in logged in only directory

I’m trying to display a javadoc in my site. It’s contained in a directory and is made up of html, css and javascript so it has it’s own navigation and menu that i want users to see in a seperate window from the site.

Want it to be restricted to people logged in to the site though. no direct linking. How can i do this? I’m thinking if logged in as php in it’s index file and .htaccess. Not sure though. Help please