suggestions wrt. JWK "alg" and "use" fields

[panva]

Since Ed keys can only be used for signatures (and have one dedicated JWS "alg" identifier) and X can only be used for ECDH (meaning not the WebCrypto algorithm identifier here) the following operation steps should be added. The alg ones I think for sure, the use ones I'll leave to a discussion.

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Ed25519 JWK importKey operation

Add a step

If the alg field of jwk is present and not "EdDSA", then throw a DataError.

---

Ed448 JWK importKey operation

Add a step

If the alg field of jwk is present and not "EdDSA", then throw a DataError.

---

Ed25519 JWK exportKey operation

Add steps

Set the alg attribute of jwk to "EdDSA". Set the use attribute of jwk to "sig".

---

Ed448 JWK exportKey operation

Add steps

Set the alg attribute of jwk to "EdDSA". Set the use attribute of jwk to "sig".

---

X25519 JWK exportKey operation

Add a step

Set the use attribute of jwk to "enc".

---

X448 JWK exportKey operation

Add a step

Set the use attribute of jwk to "enc".

[twiss]

Yeah, I definitely agree we should add the alg field, thanks for catching that.

The use attribute I don't think we should set, as the Web Crypto spec currently doesn't do so either for any of the algorithms (while it does check them on import; I assume the intention was to have the key_ops field fulfill the same role for exported keys).

[panva]

I'll remove the use commits from my PR

[panva]

3 updated.