Implementing Webhook Logic

public DeliveryResult deliver(Subscription sub, Event e) {
    var body = mapper.writeValueAsBytes(e);
    var sig  = sign(sub.secret(), body, e.id(), Instant.now());
    var req  = HttpRequest.newBuilder(URI.create(sub.url()))
        .header("Content-Type", "application/json")
        .header("X-Signature", sig)
        .header("X-Event-Id", e.id())
        .timeout(Duration.ofSeconds(10))
        .POST(BodyPublishers.ofByteArray(body))
        .build();
    var resp = httpClient.send(req, BodyHandlers.discarding());
    return new DeliveryResult(resp.statusCode(), resp.headers());
}

String stringToSign = timestamp + "." + new String(body, UTF_8);
byte[] mac = hmacSha256(secret.getBytes(), stringToSign.getBytes());
String header = "t=" + timestamp + ",v1=" + Hex.encode(mac);