[user]
email = john@example.com
name = John Doe
[url "git@github.com-corp"]
insteadOf = git@github.com
Now all repos under the path /home/john/corp/ will use that config. Then you can put a new host in your SSH config:
Host github.com-corp
HostName github.com
User git
IdentityFile /home/john/.ssh/corp_github
This way you can have different e-mail address and name in your commit messages as well.
Due to the nature of git you can't scope it via GH URL (you can have many remotes in the same local repo). Though you can still manually rewrite when you add a remote with just the SSH config change, e.g.
I guess if you have a more complex matrix of personas and remote servers (not only GH), structure and predictability becomes more important than terseness.
In the example, fnord77 posted, you can replace all the places that they used personal.github.com. It will be usable anywhere you would use ssh, including when going through a few tools that ultimately resolve to an ssh invocation. I won't copy the host block in .ssh/config but you could, for example:
`sshuttle -r my-cloud-server 0/0` for a poor man's vpn
`ssh some-enterprise-server` for when the server has a user unfriendly domain name that you don't want to bother remembering
`git clone git@github-personal:myusername/somerepo.git` when you want to clone using your personal key from GitHub.
There is the caveat, though, that you may have some nested dependencies that will use the plain ole every day host name in which case things will break for you. It rarely comes up, though, in my experience.
This is a limitation that I haven't really found a way through. I haven't tried too hard though because I've found that I can often just let the complicating set up have the 'plain' github.com host and use the custom host for the other set up. If I found that both professionally and personally I needed submodules, though, I'd probably be in trouble.
Also, if the submodules are public, the plain host will work fine because it doesn't matter what key you authenticate with.
Due to the nature of git you can't scope it via GH URL (you can have many remotes in the same local repo). Though you can still manually rewrite when you add a remote with just the SSH config change, e.g.