The authentication parts uses a standard w3c developed format called DID. en.wikipedia.org/wiki/Decentralized_identifier it’s basically a more general form of a url that must point to a specially formatted file. There are several did methods. atproto supports did:web which stores the doc at a user-set http URL path, and also did:PLC which stores the doc in a special database controlled by bsky inc.

the former method is fully independent of bsky inc