Verification

Verify webhook signatures to ensure incoming events are authentic.

Prerequisites

You will need:

A webhook subscription secret from Subscriptions
Access to the raw, unmodified request body in your webhook handler
The X-Hook0-Signature request header

Verify signatures

Verify webhook signatures to ensure that requests are authentic. This protects your application from forged webhooks and potential security threats.

How signature verification works

When you create a webhook subscription, the response includes a secret. This secret is used to verify that incoming webhooks are authentic. Each webhook request includes an X-Hook0-Signature header containing:

t field - the timestamp
h field - list of headers included in the signature
v1 field - the signature

Verification implementation

Here’s an example of how to verify webhook signatures:

import crypto from "crypto";

type HeadersMap = Record<string, string>;

function verifyWebhookSignature(
  payload: string,
  signatureHeader: string,
  secret: string,
  headers: HeadersMap,
  maxAgeMinutes = 5
): boolean {
  try {
    const elements = signatureHeader.split(",");
    const timestamp = elements.find((e) => e.startsWith("t="))?.split("=")[1] ?? "";
    const headerNames = elements.find((e) => e.startsWith("h="))?.split("=")[1] ?? "";
    const providedSignature = elements.find((e) => e.startsWith("v1="))?.split("=")[1] ?? "";

    const headerNameList = headerNames.split(" ");
    const headerValues = headerNameList.map((name) => headers[name] ?? "").join(".");

    const signedPayload = `${timestamp}.${headerNames}.${headerValues}.${payload}`;
    const expectedSignature = crypto
      .createHmac("sha256", secret)
      .update(signedPayload, "utf8")
      .digest("hex");

    const signaturesMatch = crypto.timingSafeEqual(
      Buffer.from(expectedSignature, "hex"),
      Buffer.from(providedSignature, "hex")
    );

    const webhookTime = parseInt(timestamp, 10) * 1000;
    const currentTime = Date.now();
    const ageMinutes = (currentTime - webhookTime) / (1000 * 60);

    if (ageMinutes > maxAgeMinutes) {
      console.error(
        `Webhook timestamp exceeds maximum age: ${ageMinutes.toFixed(1)} minutes > ${maxAgeMinutes} minutes`
      );
      return false;
    }

    return signaturesMatch;
  } catch (error) {
    console.error("Webhook verification error:", error);
    return false;
  }
}

import hashlib
import hmac
import time

def verify_webhook_signature(payload, signature_header, secret, headers, max_age_minutes=5):
    """Verify webhook signature and timestamp."""
    try:
        elements = signature_header.split(",")
        timestamp = next(e for e in elements if e.startswith("t=")).split("=", 1)[1]
        header_names = next(e for e in elements if e.startswith("h=")).split("=", 1)[1]
        provided_signature = next(e for e in elements if e.startswith("v1=")).split("=", 1)[1]

        header_name_list = header_names.split(" ")
        header_values = ".".join(headers.get(name, "") for name in header_name_list)

        signed_payload = f"{timestamp}.{header_names}.{header_values}.{payload}"
        expected_signature = hmac.new(
            secret.encode("utf-8"),
            signed_payload.encode("utf-8"),
            hashlib.sha256,
        ).hexdigest()

        signatures_match = hmac.compare_digest(expected_signature, provided_signature)

        webhook_time_ms = int(timestamp) * 1000
        current_time_ms = int(time.time() * 1000)
        age_minutes = (current_time_ms - webhook_time_ms) / (1000 * 60)

        if age_minutes > max_age_minutes:
            print(
                f"Webhook timestamp exceeds maximum age: {age_minutes:.1f} minutes > {max_age_minutes} minutes"
            )
            return False

        return signatures_match
    except Exception as error:
        print(f"Webhook verification error: {error}")
        return False

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"strconv"
	"strings"
	"time"
)

func verifyWebhookSignature(payload, signatureHeader, secret string, headers map[string]string, maxAgeMinutes int) bool {
	elements := strings.Split(signatureHeader, ",")
	var timestamp, headerNames, providedSignature string
	for _, element := range elements {
		if strings.HasPrefix(element, "t=") {
			timestamp = strings.TrimPrefix(element, "t=")
		}
		if strings.HasPrefix(element, "h=") {
			headerNames = strings.TrimPrefix(element, "h=")
		}
		if strings.HasPrefix(element, "v1=") {
			providedSignature = strings.TrimPrefix(element, "v1=")
		}
	}

	headerNameList := strings.Split(headerNames, " ")
	headerValues := make([]string, 0, len(headerNameList))
	for _, name := range headerNameList {
		headerValues = append(headerValues, headers[name])
	}

	signedPayload := fmt.Sprintf("%s.%s.%s.%s", timestamp, headerNames, strings.Join(headerValues, "."), payload)
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(signedPayload))
	expectedSignature := hex.EncodeToString(mac.Sum(nil))

	signaturesMatch := hmac.Equal([]byte(expectedSignature), []byte(providedSignature))

	webhookTime, err := strconv.ParseInt(timestamp, 10, 64)
	if err != nil {
		return false
	}
	ageMinutes := float64(time.Now().UnixMilli()-webhookTime*1000) / (1000 * 60)
	if ageMinutes > float64(maxAgeMinutes) {
		fmt.Printf("Webhook timestamp exceeds maximum age: %.1f minutes > %d minutes\n", ageMinutes, maxAgeMinutes)
		return false
	}

	return signaturesMatch
}

require "openssl"

def verify_webhook_signature(payload, signature_header, secret, headers, max_age_minutes = 5)
  elements = signature_header.split(",")
  timestamp = elements.find { |e| e.start_with?("t=") }&.split("=", 2)&.last.to_s
  header_names = elements.find { |e| e.start_with?("h=") }&.split("=", 2)&.last.to_s
  provided_signature = elements.find { |e| e.start_with?("v1=") }&.split("=", 2)&.last.to_s

  header_values = header_names.split(" ").map { |name| headers[name] || "" }.join(".")
  signed_payload = "#{timestamp}.#{header_names}.#{header_values}.#{payload}"
  expected_signature = OpenSSL::HMAC.hexdigest("SHA256", secret, signed_payload)

  signatures_match = expected_signature.bytesize == provided_signature.bytesize &&
    expected_signature.bytes.zip(provided_signature.bytes).reduce(0) { |acc, (a, b)| acc | (a ^ b) }.zero?

  webhook_time = timestamp.to_i * 1000
  age_minutes = (Time.now.to_i * 1000 - webhook_time) / (1000.0 * 60.0)
  if age_minutes > max_age_minutes
    puts "Webhook timestamp exceeds maximum age: #{age_minutes.round(1)} minutes > #{max_age_minutes} minutes"
    return false
  end

  signatures_match
rescue StandardError => error
  puts "Webhook verification error: #{error}"
  false
end

<?php
function verifyWebhookSignature($payload, $signatureHeader, $secret, $headers, $maxAgeMinutes = 5): bool
{
    $elements = explode(",", $signatureHeader);
    $timestamp = "";
    $headerNames = "";
    $providedSignature = "";

    foreach ($elements as $element) {
        if (str_starts_with($element, "t=")) {
            $timestamp = substr($element, 2);
        }
        if (str_starts_with($element, "h=")) {
            $headerNames = substr($element, 2);
        }
        if (str_starts_with($element, "v1=")) {
            $providedSignature = substr($element, 3);
        }
    }

    $headerNameList = explode(" ", $headerNames);
    $headerValues = array_map(
        fn($name) => $headers[$name] ?? "",
        $headerNameList
    );

    $signedPayload = $timestamp . "." . $headerNames . "." . implode(".", $headerValues) . "." . $payload;
    $expectedSignature = hash_hmac("sha256", $signedPayload, $secret);

    $signaturesMatch = hash_equals($expectedSignature, $providedSignature);

    $webhookTimeMs = intval($timestamp) * 1000;
    $currentTimeMs = intval(microtime(true) * 1000);
    $ageMinutes = ($currentTimeMs - $webhookTimeMs) / (1000 * 60);

    if ($ageMinutes > $maxAgeMinutes) {
        echo "Webhook timestamp exceeds maximum age: {$ageMinutes} minutes > {$maxAgeMinutes} minutes\n";
        return false;
    }

    return $signaturesMatch;
}

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.time.Instant;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class WebhookVerifier {
    public static boolean verifyWebhookSignature(
        String payload,
        String signatureHeader,
        String secret,
        Map<String, String> headers,
        int maxAgeMinutes
    ) {
        try {
            String[] elements = signatureHeader.split(",");
            String timestamp = "";
            String headerNames = "";
            String providedSignature = "";
            for (String element : elements) {
                if (element.startsWith("t=")) {
                    timestamp = element.substring(2);
                } else if (element.startsWith("h=")) {
                    headerNames = element.substring(2);
                } else if (element.startsWith("v1=")) {
                    providedSignature = element.substring(3);
                }
            }

            String[] headerNameList = headerNames.split(" ");
            StringBuilder headerValues = new StringBuilder();
            for (int i = 0; i < headerNameList.length; i++) {
                if (i > 0) {
                    headerValues.append(".");
                }
                headerValues.append(headers.getOrDefault(headerNameList[i], ""));
            }

            String signedPayload = String.join(".", timestamp, headerNames, headerValues.toString(), payload);
            Mac mac = Mac.getInstance("HmacSHA256");
            mac.init(new SecretKeySpec(secret.getBytes(StandardCharsets.UTF_8), "HmacSHA256"));
            byte[] expectedBytes = mac.doFinal(signedPayload.getBytes(StandardCharsets.UTF_8));
            String expectedSignature = bytesToHex(expectedBytes);

            boolean signaturesMatch = MessageDigest.isEqual(
                expectedSignature.getBytes(StandardCharsets.UTF_8),
                providedSignature.getBytes(StandardCharsets.UTF_8)
            );

            long webhookTimeMs = Long.parseLong(timestamp) * 1000;
            long currentTimeMs = Instant.now().toEpochMilli();
            double ageMinutes = (currentTimeMs - webhookTimeMs) / (1000.0 * 60.0);
            if (ageMinutes > maxAgeMinutes) {
                System.out.printf(
                    "Webhook timestamp exceeds maximum age: %.1f minutes > %d minutes%n",
                    ageMinutes,
                    maxAgeMinutes
                );
                return false;
            }

            return signaturesMatch;
        } catch (Exception error) {
            System.out.println("Webhook verification error: " + error);
            return false;
        }
    }

    private static String bytesToHex(byte[] bytes) {
        StringBuilder hex = new StringBuilder(bytes.length * 2);
        for (byte b : bytes) {
            hex.append(String.format("%02x", b));
        }
        return hex.toString();
    }

    public static void main(String[] args) {
        Map<String, String> headers = new HashMap<>();
        verifyWebhookSignature("payload", "t=0,h=host,v1=signature", "secret", headers, 5);
    }
}

And in your application:

import express from "express";

const app = express();

// Important: Get raw body for signature verification
app.use(express.raw({ type: "application/json" }));

app.post("/webhook", (req, res) => {
  const payload = req.body.toString();
  const signature = req.headers["x-hook0-signature"];
  const secret = process.env.WEBHOOK_SECRET ?? "";

  if (verifyWebhookSignature(payload, String(signature || ""), secret, req.headers as Record<string, string>)) {
    const event = JSON.parse(payload);

    // Handle your transfer event here

    res.status(200).send("OK");
    return;
  }

  res.status(400).send("Invalid signature");
});

import os
from flask import Flask, request

app = Flask(__name__)

@app.post("/webhook")
def webhook():
    payload = request.get_data(as_text=True)
    signature = request.headers.get("X-Hook0-Signature", "")
    secret = os.environ.get("WEBHOOK_SECRET", "")

    if verify_webhook_signature(payload, signature, secret, request.headers):
        event = request.get_json()

        # Handle your transfer event here

        return ("OK", 200)

    return ("Invalid signature", 400)

package main

import (
	"io"
	"net/http"
	"os"
	"strings"
)

func webhookHandler(w http.ResponseWriter, r *http.Request) {
	payloadBytes, _ := io.ReadAll(r.Body)
	payload := string(payloadBytes)
	signature := r.Header.Get("X-Hook0-Signature")
	secret := os.Getenv("WEBHOOK_SECRET")

	headers := map[string]string{}
	for name := range r.Header {
	headers[strings.ToLower(name)] = r.Header.Get(name)
	}
if _, ok := headers["host"]; !ok {
	headers["host"] = r.Host
}

	if verifyWebhookSignature(payload, signature, secret, headers, 5) {
		// Handle your transfer event here
		w.WriteHeader(http.StatusOK)
		w.Write([]byte("OK"))
		return
	}

	http.Error(w, "Invalid signature", http.StatusBadRequest)
}

require "sinatra"

post "/webhook" do
  payload = request.body.read
  signature = request.env["HTTP_X_HOOK0_SIGNATURE"] || ""
  secret = ENV.fetch("WEBHOOK_SECRET", "")
  headers = { "host" => request.host }

  if verify_webhook_signature(payload, signature, secret, headers)
    # Handle your transfer event here
    status 200
    body "OK"
  else
    status 400
    body "Invalid signature"
  end
end

<?php
$payload = file_get_contents("php://input");
$signature = $_SERVER["HTTP_X_HOOK0_SIGNATURE"] ?? "";
$secret = getenv("WEBHOOK_SECRET") ?: "";

$headers = [];
foreach ($_SERVER as $key => $value) {
    if (str_starts_with($key, "HTTP_")) {
        $headerName = strtolower(str_replace("_", "-", substr($key, 5)));
        $headers[$headerName] = $value;
    }
}
if (!array_key_exists("host", $headers)) {
    $headers["host"] = $_SERVER["HTTP_HOST"] ?? "";
}

if (verifyWebhookSignature($payload, $signature, $secret, $headers)) {
    // Handle your transfer event here
    http_response_code(200);
    echo "OK";
} else {
    http_response_code(400);
    echo "Invalid signature";
}

import static spark.Spark.port;
import static spark.Spark.post;

import java.util.HashMap;
import java.util.Map;

public class WebhookServer {
    public static void main(String[] args) {
        port(3000);

        post("/webhook", (request, response) -> {
            String payload = request.body();
            String signature = request.headers("X-Hook0-Signature");
            String secret = System.getenv().getOrDefault("WEBHOOK_SECRET", "");

            Map<String, String> headers = new HashMap<>();
            for (String headerName : request.headers()) {
                headers.put(headerName.toLowerCase(), request.headers(headerName));
            }

            if (WebhookVerifier.verifyWebhookSignature(payload, signature, secret, headers, 5)) {
                // Handle your transfer event here
                response.status(200);
                return "OK";
            }

            response.status(400);
            return "Invalid signature";
        });
    }
}

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Prerequisites

Verify signatures

How signature verification works

Verification implementation

​Prerequisites

​Verify signatures

​How signature verification works

​Verification implementation

Prerequisites

Verify signatures

How signature verification works

Verification implementation