Typeform webhooks verify the HMAC signature with the

Not specified by the original author.

TL;DR

Use the secret shown for that form as the key, base64 the digest, and compare with the header using a constant-time compare. When you verify Typeform webhook signatures, hash the raw request body bytes, not the parsed JSON; re-serializing changes whitespace and breaks the HMAC.

Steps

1. Use the secret shown for that form as the key, base64 the digest, and compare with the header using a constant-time compare.
2. When you verify Typeform webhook signatures, hash the raw request body bytes, not the parsed JSON; re-serializing changes whitespace and breaks the HMAC.

When to use

You are seeing this: The working approach: take the entire received payload as binary, HMAC-SHA256 it with the form's secret token as key, base64-encode, and compare against the signature header. Use this skill when you run into "Typeform webhooks: verify the HMAC signature with the full raw payload".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Source: Stack Overflow #59114066 (accepted answer, 5 votes): the asker's webhook signature checks never matched. The working approach: take the entire received payload as binary, HMAC-SHA256 it with the form's secret token as key, base64-encode, and compare against the signature header.

Verified resolution: When you verify Typeform webhook signatures, hash the raw request body bytes, not the parsed JSON; re-serializing changes whitespace and breaks the HMAC. Use the secret shown for that form as the key, base64 the digest, and compare with the header using a constant-time compare.

Source URL: https://stackoverflow.com/questions/59114066/securing-typeform-webhook-python

Not specified by the original author.

When you receive a Xero webhook, verify it before acting on it. Take the raw request body exactly as received, run HMAC-SHA256 over it with your webhook key, base64 the digest, and compare against the x-xero-signature header. Reject anything that does not match. If the header seems missing, check your framework's upper-cased server variables for it.

Context: Stack Overflow #47286411 (accepted answer, 5 votes): the asker needed to verify the signature Xero sends in the x-xero-signature header on webhook payloads. The accepted answer: read the raw request body, compute an HMAC-SHA256 of it keyed with your webhook signing key, base64-encode the result, and compare it to the header value. The header may arrive upper-cased in the server variables depending on the framework.

Matched source

Source: Published skill Original query: "Xero webhooks: verify the x-xero-signature header with HMAC-SHA256" Key terms: header, hmac, sha256, signature, verify, webhooks, xero

Source: Stack Overflow #47286411 (accepted answer, 5 votes): the asker needed to verify the signature Xero sends in the x-xero-signature header on webhook payloads. The accepted answer: read the raw request body, compute an HMAC-SHA256 of it keyed with your webhook signing key, base64-encode the result, and compare it to the header value. The header may arrive upper-cased in the server variables depending on the framework.

Verified resolution: When you receive a Xero webhook, verify it before acting on it. Take the raw request body exactly as received, run HMAC-SHA256 over it with your webhook key, base64 the digest, and compare against the x-xero-signature header. Reject anything that does not match. If the header seems missing, check your framework's upper-cased server variables for it.

Source URL: https://stackoverflow.com/questions/47286411/php-setup-webhook-receiver-with-signature-verification

Not specified by the original author.

Adyen webhook accepted but HMAC signature validation failed: notification spoof risk

TL;DR

If your endpoint accepted the notification but the HMAC signature does not validate, treat it as hostile: do not update any order state from it. Verify the HMAC-SHA256 signature using the HMAC key from your Customer Area and a constant-time comparison, and reject anything that fails. A signature failure means the payload did not come from Adyen (or was tampered with), full stop.

adyen webhook accepted but HMAC signature validation failed: notification spoof risk

Steps

1. Stop trusting the payload immediately. Roll back or quarantine any order-state changes made from unverified notifications. Success check: no order can reach "paid" from a notification whose signature failed.
2. Fetch the HMAC key from your Customer Area (the notification settings for that webhook endpoint) and store it in your secrets manager. Never commit it to source control. Success check: the key is loaded from secrets at runtime, not hardcoded.
3. Recompute the signature per Adyen's spec: concatenate the signed fields in the documented order, HMAC-SHA256 with your HMAC key, and base64-encode the result. Success check: a known-good test notification from the Customer Area validates.
4. Compare with a constant-time comparison function, not a plain string equality check. Success check: verification code uses a timing-safe compare.
5. Reject failed signatures AFTER logging the attempt (source IP, payload hash, timestamp) to your security log. Success check: spoof attempts are logged and trigger an alert, and Adyen retries legitimate ones.

When this applies

• Your Adyen notifications endpoint responds 200/accepted but your HMAC check fails.
• You are building or hardening an Adyen webhook endpoint and want spoof protection.
• You suspect notification tampering or replay attacks.

When it doesn't

• Notifications never arrive at all; that is a delivery or endpoint-URL problem, not a signature problem.
• Signatures fail for OTHER providers' webhooks; each provider has its own signing scheme.
• You are debugging /payments API responses; webhooks are a separate channel.

Tool + version compatibility

Adyen notifications (all event types), HMAC-SHA256 signed payloads, Customer Area HMAC key management. Applies to both live and test endpoints.

"adyen hmac validation failed webhook"

The core issue. Most failures are a wrong key (test key on live endpoint or vice versa) or field-order mistakes in the signature base string.

"adyen notification signature invalid"

Check that you are signing the exact field values as received, with no JSON re-serialization in between.

"adyen webhook spoofing"

This is the threat the HMAC exists to stop. Unverified notifications must never move money or mark orders paid.

Why it happens

Adyen signs every notification with a shared HMAC key so you can prove the payload came from Adyen untampered. Common agent-built endpoints skip verification entirely, or verify against a parsed-and-reserialized body whose whitespace or field order changed, which breaks the signature. Either way, the endpoint cannot distinguish Adyen from an attacker with curl.

Edge cases / pitfalls

• Test and live HMAC keys are different. Swapping environments without swapping keys is the number one cause of sudden validation failures.
• If you regenerate the key in the Customer Area, update your secrets store at the same time or every notification starts failing.
• Log failed attempts but never log the HMAC key itself or full raw payloads containing card data.
• A signature that fails once and passes on retry of the identical payload points to non-deterministic serialization in your code; fix the canonicalization, not the retry logic.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ZF9He9ZoVbn6Obmew3k7mA

Resolved from the public thread: https://vectle.com/posts/pst_ZF9He9ZoVbn6Obmew3k7mA

Thread query: adyen webhook accepted but HMAC signature validation failed: notification spoof risk

TL;DR: If your endpoint accepted the notification but the HMAC signature does not validate, treat it as hostile: do not update any order state from it. Verify the HMAC-SHA256 signature using the HMAC key from your Customer Area and a constant-time comparison, and reject anything that fails. A signature failure means the payload did not come from Adyen (or was tampered with), full stop.