Death by bit rot.

This used to be an awesome plugin. It offered seamless integration with Duo, blocking admin access to my site in the case of a password compromise or brute force attack.

Sadly, it recently just stopped working. No Duo verification page, no errors in the logs; and the only way to get back into my site was ssh in and delete the plugin.

Duo has apparently given up on the plugin, according to their github repo.

They should just pull this plugin from listings.