The [PPA homepage](https://launchpad.net/~broder/+archive/scripts-http-mods) includes instructions on how to install the PPA on your system, but if you're on Ubuntu Karmic or later, you can just run:
- # add-apt-repository ppa:broder/scripts-http-mods
+ # add-apt-repository ppa:broder/scripts-http-mods ; apt-get update
Once you've installed the PPA, you want to install the libapache2-mod-auth-sslcert and libapache2-mod-authz-afsgroup packages.