In ActivityPub, usually you'd refer to a person by their actor URI. But when dealing with VCS repos, we get a different representation of identity. For example, in Git usually the author of a commit looks like Jane Doe <firstname.lastname@example.org>. The identifying detail is the email address.
Jane Doe <email@example.com>
The current situation, I suppose, is that a forge grabs the commit author's email address and checks if there's a user with that email address. The email address can be used to grab the user's Libravatar etc., and to verify that the user's email address is associated with the GPG key that signs the commit, if the commit is signed.
How do we do this on the Fediverse? There's no global index matching email addresses to ActivityPub actors.
How can this be done in Git? And in Darcs? And in other VCSs?