Implement a webhook receiver

Content-Type: application/json
YCloud-Signature: t=1762224357,s=SIGNATURE_HEX
X-Webhook-Endpoint-ID: WEBHOOK_ENDPOINT_ID

import crypto from "node:crypto";

export function verifySignature(rawBody, header, secret, now = Date.now()) {
  if (!Buffer.isBuffer(rawBody) || typeof header !== "string" || !secret) return false;
  const fields = header.split(",").map(part => part.trim().split("="));
  const timestamps = fields.filter(([key]) => key === "t").map(([, value]) => value);
  const signatures = fields.filter(([key]) => key === "s").map(([, value]) => value);
  if (timestamps.length !== 1 || !/^\d+$/.test(timestamps[0])) return false;
  const timestamp = timestamps[0];
  if (Math.abs(Math.floor(now / 1000) - Number(timestamp)) > 300) return false;
  const expected = crypto.createHmac("sha256", secret)
    .update(timestamp + ".")
    .update(rawBody)
    .digest();
  return signatures.some(signature =>
    typeof signature === "string" && /^[a-fA-F0-9]{64}$/.test(signature) &&
    crypto.timingSafeEqual(expected, Buffer.from(signature, "hex"))
  );
}

import express from "express";
import { verifySignature } from "./signature.js";
import { persistEvent } from "./event-inbox.js";

const app = express();
const secret = process.env.YCLOUD_WEBHOOK_SECRET;
if (!secret) throw new Error("YCLOUD_WEBHOOK_SECRET is required");

// Register the raw-body route before any JSON-parsing middleware.
app.post("/webhook", express.raw({ type: "application/json", limit: "1mb" }), async (req, res) => {
  if (!verifySignature(req.body, req.get("YCloud-Signature"), secret)) {
    return res.sendStatus(401);
  }
  let event;
  try {
    event = JSON.parse(req.body.toString("utf8"));
  } catch {
    return res.sendStatus(400);
  }
  if (!event || typeof event.id !== "string" || typeof event.type !== "string") {
    return res.sendStatus(400);
  }
  try {
    await persistEvent(event.id, event);
    return res.sendStatus(204);
  } catch {
    return res.sendStatus(503);
  }
});

app.listen(3000);

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.time.Instant;
import java.util.HexFormat;

@RestController
public class WebhookController {
    private final String secret;
    private final ObjectMapper mapper;
    private final EventInbox inbox;

    public WebhookController(@Value("${YCLOUD_WEBHOOK_SECRET}") String secret,
                             ObjectMapper mapper, EventInbox inbox) {
        if (secret.isBlank()) throw new IllegalArgumentException("Missing webhook secret");
        this.secret = secret;
        this.mapper = mapper;
        this.inbox = inbox;
    }

    @PostMapping("/webhook")
    public ResponseEntity<Void> receive(
            @RequestHeader(value = "YCloud-Signature", required = false) String header,
            @RequestBody byte[] body) {
        if (!verify(body, header)) return ResponseEntity.status(401).build();
        JsonNode event;
        try {
            event = mapper.readTree(body);
            if (event == null || !event.path("id").isTextual() || !event.path("type").isTextual()) {
                return ResponseEntity.badRequest().build();
            }
        } catch (Exception invalidJson) {
            return ResponseEntity.badRequest().build();
        }
        try {
            inbox.insertIfAbsent(event.path("id").asText(), body);
            return ResponseEntity.noContent().build();
        } catch (Exception storageFailure) {
            return ResponseEntity.status(503).build();
        }
    }

    private boolean verify(byte[] body, String header) {
        if (header == null) return false;
        String timestamp = null;
        java.util.List<String> signatures = new java.util.ArrayList<>();
        for (String part : header.split(",")) {
            String[] pair = part.trim().split("=", 2);
            if (pair.length != 2) continue;
            if (pair[0].equals("t")) {
                if (timestamp != null) return false;
                timestamp = pair[1];
            }
            if (pair[0].equals("s")) signatures.add(pair[1]);
        }
        if (timestamp == null || !timestamp.matches("[0-9]{1,12}")) return false;
        try {
            long age = Instant.now().getEpochSecond() - Long.parseLong(timestamp);
            if (Math.abs(age) > 300) return false;
            Mac mac = Mac.getInstance("HmacSHA256");
            mac.init(new SecretKeySpec(secret.getBytes(StandardCharsets.UTF_8), "HmacSHA256"));
            mac.update((timestamp + ".").getBytes(StandardCharsets.UTF_8));
            byte[] expected = mac.doFinal(body);
            for (String signature : signatures) {
                if (signature.matches("[a-fA-F0-9]{64}") &&
                    MessageDigest.isEqual(expected, HexFormat.of().parseHex(signature))) return true;
            }
            return false;
        } catch (Exception invalidSignature) {
            return false;
        }
    }

    public interface EventInbox {
        void insertIfAbsent(String eventId, byte[] eventBody) throws Exception;
    }
}