login_skey(8) on OpenBSD
The text afdd8c176b9b, as OpenBSD 6.4, OpenBSD 6.3, OpenBSD 6.2, OpenBSD 6.1, OpenBSD 6.0, OpenBSD 5.9, OpenBSD 5.8, OpenBSD 5.7, OpenBSD 5.6, OpenBSD 5.5, OpenBSD 5.4, OpenBSD 5.3, OpenBSD 5.2, OpenBSD 5.1 shipped it.
provide S/Key authentication type