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AccessOwl signs every webhook request using RFC 9421 HTTP Message Signatures. The signing scheme used is Ed25519 (asymmetric). Each request includes three headers you can use for verification:
HeaderDescription
Content-DigestSHA-512 hash of the request body, formatted as sha-512=:BASE64:
Signature-InputDescribes which request components were signed, the creation timestamp, and the key ID. Example: sig=("@target-uri" "content-digest" "content-type" "idempotency-key");created=1718884473;keyid="whsec_abc123"
SignatureThe actual signature over the covered components, formatted as sig=:BASE64:
The key ID in Signature-Input matches the whsec_... identifier shown in Settings → Webhooks, where you can also retrieve the public key to verify signatures.
It’s advised to verify the signature before processing a webhook payload. Reject any request where verification fails.

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Constructing the signature base

To verify the signature you must reconstruct the same signature base that AccessOwl signed. The procedure follows RFC 9421 §2.5:
  1. For each component listed in Signature-Input, in order, emit one line formatted as: 
    "<component-name>": <component-value>
  2. Append a final line using the exact string value of the Signature-Input header: 
    "@signature-params": <Signature-Input value>
  3. Join all lines with a single newline character (\n). There is no trailing newline.
AccessOwl always covers four components in this fixed order: @target-uri, content-digest, content-type, idempotency-key. Example signature base: 
"@target-uri": https://your-endpoint.example.com/webhook
"content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
"content-type": application/json
"idempotency-key": 018f1e2a-3b4c-7d8e-9f0a-1b2c3d4e5f6a
"@signature-params": ("@target-uri" "content-digest" "content-type" "idempotency-key");created=1718884473;keyid="whsec_abc123"
Take @target-uri from the full request URL (including scheme and path) and content-digest directly from the Content-Digest request header. Once assembled, verify the Signature header value against this base using the Ed25519 public key for your webhook endpoint, which is available in Settings → Webhooks.
We recommend using an HTTP Message Signatures library for your language rather than implementing RFC 9421 verification from scratch.

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Manual verification

If you prefer not to use a library, the examples below show how to verify signatures manually using standard cryptographic libraries.

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Setup

The public key from Settings → Webhooks is provided as a JWK. Base64-encode it and set as an environment variable: 
export ACCESSOWL_WEBHOOK_PUBLIC_KEY=$(echo '{"crv":"Ed25519","kid":"whsec_xxx","kty":"OKP","x":"..."}' | base64)

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Verification function

import { createPublicKey, verify } from 'node:crypto';

const PUBLIC_KEY_JWK = JSON.parse(
  Buffer.from(process.env.ACCESSOWL_WEBHOOK_PUBLIC_KEY, 'base64').toString()
);
const publicKey = createPublicKey({ key: PUBLIC_KEY_JWK, format: 'jwk' });

export function verifyWebhook(req) {
  const signatureInput = req.headers['signature-input'];
  const signature = req.headers['signature'];
  const contentDigest = req.headers['content-digest'];
  const contentType = req.headers['content-type'];
  const idempotencyKey = req.headers['idempotency-key'];

  // Extract base64 signature from "sig=:BASE64:" format
  const sigMatch = signature.match(/^sig=:(.+):$/);
  if (!sigMatch) throw new Error('Invalid signature format');
  const signatureBytes = Buffer.from(sigMatch[1], 'base64');

  // Extract signature-input value (after "sig=")
  const sigInputValue = signatureInput.replace(/^sig=/, '');

  // Build the signature base per RFC 9421
  const targetUri = `https://${req.headers.host}${req.url}`;
  const signatureBase = [
    `"@target-uri": ${targetUri}`,
    `"content-digest": ${contentDigest}`,
    `"content-type": ${contentType}`,
    `"idempotency-key": ${idempotencyKey}`,
    `"@signature-params": ${sigInputValue}`,
  ].join('\n');

  // Verify with Ed25519
  return verify(null, Buffer.from(signatureBase), publicKey, signatureBytes);
}

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Security considerations

HTTPS required: The examples construct @target-uri with https://. AccessOwl only delivers webhooks to HTTPS endpoints. If you’re behind a reverse proxy, ensure the Host header reflects your public hostname. Content-Digest verification: The signature covers the Content-Digest header, but you may also want to independently verify that the digest matches the actual request body to detect any tampering between signature generation and delivery. Replay protection: The Signature-Input header includes a created timestamp. Consider rejecting requests where this timestamp is more than a few minutes old to prevent replay attacks.

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Test vectors

Use these values to validate your implementation: 
Public key (JWK):
{"crv":"Ed25519","x":"7EZp3jjRy8iygjUguHNB0IaPTPU8hVyWFy2hCdbwi1s","kty":"OKP","kid":"whsec_test"}

Request:
POST https://example.com/webhook
Host: example.com
Content-Type: application/json
Content-Digest: sha-512=:/OcoCOV1JIOPCUiyfsEsOwlsIF2EoPSD4avSNJ8/ksknyitIPnudRnMBbcZF6HSaLfZO2JpNloCoRgDXbQpzZw==:
Idempotency-Key: 018f1e2a-3b4c-7d8e-9f0a-1b2c3d4e5f6a
Signature-Input: sig=("@target-uri" "content-digest" "content-type" "idempotency-key");created=1718884473;keyid="whsec_test"
Signature: sig=:Ee+jOzzCmLHHQWRglRaespo5p9x2n+YtCHIgG/oPhiSEL7HPaOTK0WepYOjaV+4HF0kziCWhALVCMt9PzkCnAw==:

Body:
{"event_type":"test","data":{}}
Verification should return true for these inputs.