Converting JWK to VAPID

[trd-sys]

Can someone recommend a reliable way to convert JWK object + JWK Pubkey to equivalent VAPID Public and Private keys? I have seen online tools that generate PEM files from JWK Object, but would prefer an offline method. Thanks.

[kndwin]

I used this script, I figured out the subarray split ranges from the offical protocol docs
https://web.dev/articles/push-notifications-web-push-protocol

const vapid = {
  publicKey:  "...",
  privateKey: "...",
};

const jwk = {
  kty: "EC",
  crv: "P-256",
  key_ops: ["sign"],
  // they skip the first byte cause '\04' indicates that the key is a raw uint8 array
  // https://github.com/web-push-libs/vapid/blob/main/js/vapid.js#L116
  x: uint8ArrayToBase64Url(base64ToUint8Array(vapid.publicKey).subarray(1, 33)),
  y: uint8ArrayToBase64Url(
    base64ToUint8Array(vapid.publicKey).subarray(33, 65)
  ),
  d: vapid.privateKey,
};

console.log({
  jwk,
});

function uint8ArrayToBase64Url(uint8Array: Uint8Array) {
  return btoa(String.fromCharCode.apply(null, uint8Array))
    .replace(/\+/g, "-")
    .replace(/\//g, "_")
    .replace(/=+$/, "");
}

function base64ToUint8Array(base64String: string) {
  const padding = "=".repeat((4 - (base64String.length % 4)) % 4);
  const base64 = (base64String + padding).replace(/-/g, "+").replace(/_/g, "/");
  const rawData = atob(base64);
  const output = new Uint8Array(rawData.length);
  for (let i = 0; i < rawData.length; ++i) {
    output[i] = rawData.charCodeAt(i);
  }
  return output;
}