I’m glad Userify works well for you. For my purposes, whipping up a couple of cronjobs involving curl and OpenSSH is more appropriate than relying on an external cloud service.

> But I've been burned before when a central auth server was down and I couldn't log into my servers

There is no central auth server involved here. My servers check login credentials against the CA’s public key, which is installed alongside my sshd config file. I make my certificates valid for three weeks, but regenerate them every two, so if some failure happens with creating or fetching certificates I have a week to notice and fix the problem.