Summary

SubtleCrypto.wrapKey("jwk", key, wrappingKey, "AES-KW") threw TypeError: Data must be multiple of 8 bytes because the UTF-8 JSON serialization of a JWK is generally not aligned to 8 bytes, which AES-KW requires.

Pad the JWK JSON with ASCII spaces (0x20) to the next multiple of 8 before passing to AES-KW. This matches the de-facto behavior of Node.js, Chrome, and Firefox (the spec is silent here, but every implementation pads). The unwrap path needs no change — JSON.parse accepts the trailing whitespace produced after AES-KW unwrap.

Repro from the issue now matches Node.js output:

const { subtle } = globalThis.crypto;
const [key, wrappingKey] = await Promise.all([
  subtle.generateKey({ name: "HMAC", hash: "SHA-512" }, true, ["sign", "verify"]),
  subtle.generateKey({ name: "AES-KW", length: 256 }, true, ["wrapKey", "unwrapKey"]),
]);
const wrapped = await subtle.wrapKey("jwk", key, wrappingKey, "AES-KW");
const unwrapped = await subtle.unwrapKey(
  "jwk", wrapped, wrappingKey, "AES-KW",
  { name: "HMAC", hash: "SHA-512" }, true, ["sign", "verify"],
);
// wrapped is now a 256-byte ArrayBuffer; unwrapped is a usable HMAC CryptoKey

Fixes #35416.

Test plan

• cargo test -p unit_tests --test unit -- webcrypto — webcrypto_test and webcrypto_mldsa_test pass
• cargo test -p deno_crypto — all crate tests pass
• cargo clippy -p deno_crypto — clean
• Added regression test testWrapUnwrapJwkAesKw covering all four HMAC hashes (SHA-1/256/384/512); verifies wrapped length is a multiple of 8 and that the unwrapped key produces the same MAC as the original
• Manual repro from the issue now runs without TypeError and matches the Node.js output shape (256-byte ArrayBuffer for HMAC SHA-512)