import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

static byte[] hmacSHA256(byte[] message, byte[] key) ctex {
  S algorithm = "HmacSHA256";
  Mac mac = Mac.getInstance(algorithm);
  mac.init(new SecretKeySpec(key, algorithm));
  ret mac.doFinal(message);
}

static byte[] hmacSHA256(S message, byte[] key) {
  ret hmacSHA256(toUtf8(message), key);
}