I just checked in a commit where 2 factor seems to be working pretty smoothely within Chell. The biggest hurdle was figuring out how PhalconPHP would have to load this class. Since Phalcon’s pretty well documented, it was easy enough to expend the (auto)loader a bit for the Duo PHP class.
After that I just had to do some small refactor on the login methods. Easy enough to set things up, and since Duo is free for home/personal use, it’s a good fit as well. Below a small taste of the outcome 🙂