Use the same SSH key to both connect to remote server and push to GitHub from that server

Question

I've generated an SSH key pair to log to my remote server. I've also added that same public key in GitHub. So from my own machine, I have SSH access to GitHub:

Hi hdodov! You've successfully authenticated, but GitHub does not provide shell access. Connection to github.com closed.

This means I can clone private repositories in my GitHub account on my local machine.

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Since I use the same key to authenticate to both GitHub and my server, is it possible to use that same key to clone a repo on the server, while SSH-ed to it? If I try that, I get:

[email protected]: Permission denied (publickey).

And this makes sense, because I have no private key on the remote server - it's on my local machine. But since I've used that key connect to the server in the first place, I've proven my possession of it, so shouldn't I be able to just pull from the repo?

Yes, I can just copy my private key to the server, but transferring it over the internet sounds like a bad idea to me. Or perhaps using the same key for authentication at multiple places is the bigger issue in the first place? Should I just have separate keys?

Answer 1

What you are looking for probably is:

1. Running ssh authentication agent (ssh-agent) on your ssh client machine;
2. And forwarding ssh agent connection to the server (-A commandline or ForwardAgent config file option).

This way you will be able to use the keys you have locally on host on the server without physically copying them there.

Answer 2

If AddKeysToAgent is set in ssh_config (by default it's not) or if you request it in the command line, ssh itself will add the key it uses. This means if you want to use the same key to authenticate to the server and later on the server then you don't need ssh-add. You can do:

# with agent already running ssh -A -o AddKeysToAgent=yes …