generateHmacSignature method
Implementation
String generateHmacSignature(String message) {
// String derivedKey = deriveKeyFromSecret(secretKey);
final key = utf8.encode(secretKey);
final bytes = utf8.encode(message);
final hmac = Hmac(sha256, key); // Use SHA-256 for HMAC
final digest = hmac.convert(bytes);
return digest.toString();
}