GitHub's SSH key handling is awful. A key that GitHub knows about anywhere can get SSH access. To do a read-only git clone over SSH (i.e. if you're cloning a public repo and its submodules have [email protected] URLS), your user's SSH key has to be known to GitHub somewhere, and it works. Try from a just-built dev VM, and the submodule init fails because GitHub doesn't know about the key.
So, this repo exists just so I can set random dev VM's SSH keys as "deployment keys",
just to allow those random VMs to git submodule update --init
third-party repos.