This is a plugin to the tfa framework for Duo Security.
- Download, install and enable the tfa framework
- Download, install and enable this module.
- Enable this plugin at admin/config/people/tfa
7.x-1.x uses Duo auth API to do the authentication. This may not be usable on non enterprise accounts
7.x-2.x uses their webapi, but breaks some Drupal best practice.