Every PDS is an oauth identity layer on top of DID, so every platform in the atmosphere that bundles a PDS comes with this affordance. We didn’t need to build anything, it just came with the reference PDS.
Yes, this is why ‘Login with Facebook/Google/Twitter’ has taken over the web as the default way of logging into applications.
The atmospheric answer to this is the everything-account inherent to the protocol.
Right now, for end-users what that looks like is “whichever open-social platform you signed up for first, that’s your multi-purpose account for anywhere else on the atmosphere.”
@christian.bsky.social & co. are doing critical work to advance and standardize that UX story.
Research Project for ATProto Ecosystem Brand and User Experience Needs
Users are still free to make separate accounts at their own discretion, but I see no need to make the everything-account inaccessible by design.
This is something we get essentially for free by being atproto-based. Yes, over time it also needs some dedicated design, but that’s being figured out as a community effort like the one linked above.