In another comment I went into more detail about how I keep the CA secure.
Or, just paste your public key into your Userify profile and the same thing happens in seconds for every server that you have authorization for. Even better, there's no dependency on having a CA up and running in order to be able to log in; since your account is a regular local Linux account (just managed centrally), you log directly into the server with no need for that server to confirm your login elsewhere.
But I've been burned before when a central auth server was down and I couldn't log into my servers (through no fault of my own), so I wouldn't want to go back to the old "please wait until we check your login against a central server" model again.
> 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.