Specific kid's public key. Throws on unknown or expired kid.
Active verification keys for JWKS endpoint. Remote adapters may fetch + cache.
Sign claims and return a compact JWT. The KeyStore self-injects alg
and kid into the protected header; callers may set only typ.
Remote-sign adapters (KMS/HSM) perform the remote call here.
Returns the current signing kid as a fallback for verifying legacy/malformed tokens that lack a
kidheader. Do not use for rotation-safe lookup — for rotation, pass the token's ownkidtogetVerificationKey(kid).MUST be synchronous and cheap. Remote-sign adapters (KMS/HSM) must cache the current kid locally and return it without any remote call. Never exposes private key material.