hmacSha256 function
Implementation
Uint8List hmacSha256(Uint8List hmacKey, Uint8List data) {
// HMAC SHA-256: block must be 64 bytes
final hmacResult = hmac.HMac(sha.SHA256Digest(), 64)
..init(pointy.KeyParameter(hmacKey));
return hmacResult.process(data);
}