[doublerebel]

I've been using Duo Security to add 2FA on SSH and other services on my SmartOS instances. It's really easy and the price is pretty low compared to the amount of work it would take to manage the keys and manual implementations.

In theory I could worry about Duo going down, but I also rely on other critical cloud services and do have other ways to access an instance in an emergency (and Duo supports fallbacks).

Simplicity can be deceiving. In this case I think leaving security to the pros is worth the tradeoff. I've previously relied on cloud services for secure user management and wasn't let down.