OpenID would have done it, but Facebook and Google neutered it in favour of OAuth so they could cement themselves as primary players.

It's been some time last I checked, but isn't OpenID Connect provided anymore by Goog/Fb? Why wouldn't that be a reasonable choice if you wanted a protocol that, from the dev side of things, allowed you to uniformly target external auth providers, or your own?

OoenID Connect is different. Its basically just OAuth2, and google/fb require the ap developer to register their app with google/fb in order to authenticate users.

Whcih is pretty bad for both developers and users, as a user I cant run my own identity provided and as a developer I have to spend time setting up accounts with ever identity provider i wish to integrate.

Original OpenID just let me as a user use a URL as my identity, so I could use any identity provider I wanted, including running one myself.

EDIT: There is a specification for dynamic client registration but nobody implements it as far as I've been able to tell.

Here comes SSSO! I can hardly wait!

Of course, there may be competing SSSO solutions...

We could have a Simplified Experience Single-Sign-On, or SESSO. Italian developers would adopt it enthusiastically.

If only there was a decentralized option that has already solved this... We could call it OpenID or something like that... Oh, wait..

You also have IndieAuth that is slowly gaining more adoption.

https://en.wikipedia.org/wiki/IndieAuth

https://indieauth.net/

Cool, that looks awesome, thanks!

Yes! and then I just sign in once into my single SSO signon!