singleuser sshd

This is a basic SSH server that:

1. only allows the user running the server to connect
2. only allows ssh key authentication
3. only runs in the foreground

it does not support user switching, pam, etc.

this is useful for letting untrusted ssh clients connect to a shell running in something like ajail

LLM statement

Gemini 3 wrote almost all this, but it's < 150 loc, so it's easy to review.

license

MIT