Adding authentication to certain web pages

My site currently runs with a CMS I wrote myself. The data entry pages are
protected by HTTP authentication.

I'd like to move to a more sophisticated authentication system that will
handle the creation and access for users, tie into two-factor
authentication and decide who can do what to each data entry page. I'm
looking for any pointers to established frameworks I can drop into the
pages that need protecting, suggestions for tutorials, etc.

Many, many thanks in advance.