Configuration instructions for Apache

Hi I need you to write for me simple instructions on how to set up Apache to securely serve mercurial repositories. My Apache is already configured to serve a regular website on port 80, and to serve (insecurely) the mercurial repos on port 4321. So what I need is to add the layer of requiring authentication with username/password in order to access the repos (both pull and push). Keep in mind that my configuration is on OS X, but I don't think it should matter much since both Apache and mercurial are configurable pretty much the same way as on any other system. The instructions should be accurate and clear enough so that by following them I reach the desired result without caveats.