Definitely not appropriate for protecting Real Infrastructure, but for my handful of personal machines I put my authorized keys in a Google Doc and configure hosts to download it using `AuthorizedKeysCommand`. Makes it easy to add and revoke hosts in one place, which also makes rotation possible.

I have a hardware-backed "doomsday key" to use if the Google Doc stops working.

Writeup and script at https://github.com/mmdriley/authorized_keys