auth0 is beyond awesome but currently only supports federated and SSO logins. We'd like to avoid tracking our users as much as possible but we certainly need a "login" to identify e.g. content owners or users with certain rights or enable chats, you name it.
These are really good:
https://magic.link/
https://3box.io/
https://blockstack.org/
and watch out for e.g. Polkadot / Cosmos to launch a DID based, chain independent SSI soon ;)