I wanted to ask almost this question, then saw that it is on #1 right now.

My use case is ssh. I would like to stick my private key into a local Docker container, have a ssh-identical cli that reverse proxies into the container, and have some rules about what ssh commands the container may proxy or not.

Does anyone know of something like this?

if you usecase is just about dealing with private key and txn signing why not use any KMS service?