support ed25519 and OKP key type

[TheButlah]

https://datatracker.ietf.org/doc/html/rfc8037

Even if support for the actual cryptography is deemed out of scope or too hard for now, it would be good to add the serialization support to JWK.

[dvsekhvalnov]

Hi @TheButlah ,

1. i doubt CFRG ECDH supported in .net runtimes at all, here is open issue Proposal: Add Ed25519 and Curve25519 Algorithms to System.Security.Cryptography dotnet/runtime#14741

Which leaves us with options to implement/port ourselves or reply on 3rd party library (if any). Honestly i don't like both options given and fixed different kinds of attacks on jose/jwt libs. Would really like support from runtime much more.

2. what did you mean by JWK support? Add new KeyType.OKP? Real bridging between JWK and native crypto is possible once we know what type of key object for actual crypto is used.