At work, we are migrating to use GitHub's Enterprise Managed Users (EMU), and our enterprise policy prevents enterprise users from interacting with non-enterprise repos (no PRs, no commenting on issues, etc.). So in order to contribute to OSS, we have to maintain two separate users - an enterprise one and a public one. This causes a problem when using SSH keys to authenticate - GitHub does not allow the same key to be used for multiple users, so each user has to have its own SSH key.

This then brings up the question of how to choose which key to use when connecting to github.com. With Git, it respects ~/.ssh/config, so the following setup works (just have to remember to use the appropriate host in remotes):

Host github
  HostName github.com
  User tp-woven
  IdentityFile ~/.ssh/id_ed25519
  AddKeysToAgent yes
  IdentitiesOnly yes

Host github-sg
  HostName github.com
  User <enterprise_user>
  IdentityFile ~/.ssh/id_ed25519_emu
  AddKeysToAgent yes
  IdentitiesOnly yes

However, trying to use this setup with jj results in an error:

Error: failed to resolve address for github-sg: nodename nor servname provided, or not known; class=Net (12)

@yuja suggested on Discord that I may be able to use ssh-add -h, but this does not seem to be supported on macOS.