As a bare metal cloud service provider, we built a little TUI app over ssh so that people could upload their public keys to us without having to use a web interface. It has worked out really well because it makes it possible to "upload" the public key without having to do anything but login.

We automatically configure ssh on the servers to auth against our own internal api for serving up the keys. This way, customers can add to authorized_keys and also use our TUI for management as well.