We're currently using OpenWebAuth for cross-domain access control. It's basically just http-signatures and webfinger. https://macgirvin.com/wiki/mike/OpenWebAuth/Home
For site authentication (as opposed to cross-domain authorisation) there's IndieAuth and OpenIdConnect and we're currently investigating how we might be able to work with webauthn.
I personally would prefer having integrated services rather than requiring accounts on 20-30 different services and trying to synchronise my connections across them. That's a lot of duplication of effort. But many people don't like integrated services because of the perceived added complexity. So it will be interesting to see how this current evolution of micro-services unfolds.