There are many issues related to the use of ssh agents. (see #5228). Personally, I use secretive to store an SSH key in my Github SSH key in my laptop's secure element. However, because jj uses libgit2, it isn't able to support an SSH agent whose identity socket isn't available via $SSH_AUTH_SOCK.

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

I'm trying to get libgit2/libgit2#7034 merged in libgit2 upstream. If and when it merges, it would be great if jj offered a config to specify a custom ssh agent identity socket.

Of course, when #5228 is released, I'll be able to fallback to using a git subprocess and .ssh/config override. But building this functionality straight into jj would be more straightforward.