computeJwkThumbprint

Compute the RFC 7638 JWK thumbprint ("jkt") for RSA or EC public keys.

Canonicalization rules:

EC: use members {"crv","kty","x","y"} in lexicographic order with string values.
RSA: use members {"e","kty","n"} in lexicographic order with string values.
Then UTF‑8 encode the canonical JSON and compute base64url(SHA‑256(json)).

base64url SHA‑256 thumbprint, or null when unsupported/malformed

jsonWebKey

a decoded JWK map from the DPoP header (must contain required members for RSA or EC)