If you're willing to consider PGP, there's also https://wiki.gnupg.org/WKD https://wiki.gnupg.org/WKD which provides a much neater mechanism for domain owners t

If you're willing to consider PGP, there's also https://wiki.gnupg.org/WKD https://wiki.gnupg.org/WKD which provides a much neater mechanism for domain owners to publish pub keys that can be used for identity verification too. Also somewhat intersecting with that space is https://keyoxide.org/ https://keyoxide.org/ which can provide proofs of that identity across different services.