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Every delivery is signed so you can confirm it genuinely came from Audienceful and wasn’t tampered with or replayed. Verify the signature on each incoming request before trusting its contents.

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The signature header

Each delivery carries an X-Audienceful-Signature header containing a timestamp and a signature: 
X-Audienceful-Signature: t=1751630400,v1=<hex hmac-sha256>
  • t — the Unix timestamp (seconds) when the delivery was signed.
  • v1 — the signature: the lowercase hex HMAC-SHA256 of the string {t}.{raw_request_body}, keyed with your endpoint’s signing secret.

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How to verify

  1. Read the raw request body and the X-Audienceful-Signature header.
  2. Parse t and v1 out of the header.
  3. Reject the request if t is more than 5 minutes away from your current time (replay protection).
  4. Compute HMAC-SHA256(secret, "{t}.{raw_body}") as lowercase hex.
  5. Compare your computed value against v1 using a constant-time comparison. If they match, the request is authentic.
Your signing secret (whsec_…) is returned once, when you create the endpoint.
Verify against the raw request body bytes, exactly as received — before any JSON parsing or re-serialization. Re-serializing the body (even reformatting whitespace) changes it, and the signature will no longer match. Most frameworks expose the raw body separately from the parsed JSON.

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Examples

import hashlib, hmac, time


def verify_signature(secret: str, raw_body: str, signature_header: str, tolerance: int = 300) -> bool:
    parts = dict(kv.split("=", 1) for kv in signature_header.split(","))
    timestamp = int(parts["t"])

    # Reject stale timestamps (replay protection).
    if abs(time.time() - timestamp) > tolerance:
        return False

    expected = hmac.new(
        secret.encode(), f"{timestamp}.{raw_body}".encode(), hashlib.sha256
    ).hexdigest()
    return hmac.compare_digest(expected, parts["v1"])

import crypto from "crypto";

export function verifySignature(
  secret: string,
  rawBody: string,
  signatureHeader: string,
  toleranceSeconds = 300,
): boolean {
  const parts: Record<string, string> = {};
  for (const kv of signatureHeader.split(",")) {
    const [key, value] = kv.split("=", 2);
    parts[key] = value;
  }

  const timestamp = parseInt(parts.t, 10);
  // Reject stale timestamps (replay protection).
  if (Math.abs(Date.now() / 1000 - timestamp) > toleranceSeconds) {
    return false;
  }

  const expected = crypto
    .createHmac("sha256", secret)
    .update(`${timestamp}.${rawBody}`)
    .digest("hex");

  const expectedBuf = Buffer.from(expected);
  const providedBuf = Buffer.from(parts.v1 ?? "");
  return (
    expectedBuf.length === providedBuf.length &&
    crypto.timingSafeEqual(expectedBuf, providedBuf)
  );
}

<?php

function verify_signature(string $secret, string $rawBody, string $signatureHeader, int $tolerance = 300): bool {
    $parts = [];
    foreach (explode(',', $signatureHeader) as $kv) {
        [$key, $value] = array_pad(explode('=', $kv, 2), 2, '');
        $parts[$key] = $value;
    }

    $timestamp = (int) ($parts['t'] ?? 0);
    // Reject stale timestamps (replay protection).
    if (abs(time() - $timestamp) > $tolerance) {
        return false;
    }

    $expected = hash_hmac('sha256', $timestamp . '.' . $rawBody, $secret);
    return hash_equals($expected, $parts['v1'] ?? '');
}
The same signature scheme is used by the automation “Send Webhook” action, signed with that action’s own secret — so the same verification code works there too.