Debian based container image, running openssh-daemon only accessable by user named "borg" using SSH-Publickey Auth & "borgbackup" as client. Backup-Repositoriees, client's SSH-Keys & SSHd's Hostkeys will be stored in persistent storage.
Here we will put all SSH public keys from our borg clients, we want to backup. Every key must be it's own file, containing only one line, with the key. The name of the file will become the name of the borg repository, we need for our client to connect.
That means every client get's it's own repository. So you might want to use the hostname of the client as the name of the sshkey file.
This directory will be automaticly created on first start. Also run.sh will copy the SSH-Hostkeys here, so your clients can verify it's borgservers ssh-hostkey.