hmac-sha256.js

{
  async function hmac_sha256(key, str) {
     // encode the string key as bytes using UTF8 encoding.
     const keyBytes = new TextEncoder().encode(key);
     // generate a key for use in signing with HMAC-SHA256
     const secretKey = await crypto.subtle.importKey(
       "raw", keyBytes,
       { name: "HMAC", hash: "SHA-256" },
       false, ['sign']
     );
     const messageBytes = new TextEncoder().encode(str);
     // create the raw signature
     const signature = await crypto.subtle.sign(
      "HMAC",
       secretKey,
       messageBytes
     );
     // and encode to HEX
     return new Uint8Array(signature).reduce((hex, byte) => hex + (byte < 16 ? "0": "") + byte.toString(16), "");
  }

  // example:
  const input = `{"processing_id":"123","status":"ok","result":[]}`;
  const secret = 'foobarbaz';

  hmac_sha256(secret, input).then(
    signature => console.log("Signature:", signature),
    error => console.error(error)
  );
}