i made https://git.mleku.dev/mleku/next.orly.dev/src/branch/main/docs/NIP-XX-CASHU-ACCESS-TOKENS.md which uses cashu as an auth system using a HTTP header to carry a base64 signed spend of the token, proof of control, without providing the identity, only that the user has some specific permission according to that valid token of that scope.

it's a voucher use case, there is a lot of uses for this but auth is a primary one. with this you can regulate how many users are using a relay and tier their access rights with rate limits and this can include blossom on orly, as it has integration with the running ACL policy system. i haven't extensively developed the permissions control specific to blossom yet though.