Here is an extension / plugin for mediawiki to authenticate against a Radius server. I couldn’t find one anywhere else, which is surprising. I can’t believe I am the first person to want to do this. Anyway, this is just bare bones, but it works for an internal mediawiki setup.
First, get Pure PHP radius class 1.2.2 from http://developer.sysco.ch/php. This does the actual radius authentication. Put radius.class.php in wiki/extensions/ (assuming wiki is your mediawiki install). There is probably a better place to put it, but I was setting this up for internal use and wanted to get it working quickly.
Next, create wiki/extensions/RadiusAuthPlugin.php. Make sure you fill in RADIUS_SERVER, SHARED_SECRET, and NAS_IP_ADDRESS with your actual information. Lastly, update your LocalSetup.php.
You can find the RadiusAuthPlugin.php and the part to add to LocalSetup.php in this gist: