This is baked into Git at the core, but just like many other cases, GitHub subverts the intent of fundamental expectations about the way Git is supposed to be used and actively goes out of its way to make it difficult if you're interacting with the project through GitHub instead of local tools. (In fact, for new GitHub accounts, it even defaults to obscuring users' contact info, and it attributes all changes made through the web UI to an opaque @github.com email address. You have to deliberately go into the settings to turn this off, without ever getting a notification that that's what GitHub is doing.)