I have an ssh-agent running on my local machine. I connect to a remote machine via SSH, with agent forwarding enabled. On that remote there is an instance of gpg-agent running.
I know that recent versions of gpg-agent (2.1+) have the command-line flag
--extra-socket which you can use have the agent retrieve not only the keys added to it, but also keys from a forwarded gpg-agent.
However, I don't have gpg-agent running on my local machine; I have ssh-agent. Is there a way to have gpg-agent retrieve SSH keys from that forwarded ssh-agent?