Support SSH CA Key Signing

SSH has a concept of key signing that is similar to x509 (not the same). This capability allow great control of ssh key validity by tying it to a central authentication source.

Signed host key, allows you to validate that the key is trusted without needing to verify the fingerprint.
Signed client key removes the need to maintain authorized_key files.

It would be awesome if RDM had the ability to generate/store the SSH CA key and perform key generation and signing.

This sign provides a better explanation and breakdown of how it works. https://ef.gy/hardening-ssh