I have the the plugin installed and running without an error. I made the suggested modifications (below). Now, Mediawiki pages default to the "Login Required" prompt. From what I can tell, Auth_remote_user_hook() is never called.
Any suggestions on the next step?
Oops, I probably should have told you to make sure you declare the global variable before you use it. It should be:
global $wgHooks; $wgHooks['AutoAuthenticate'][] = 'Auth_remote_user_hook';