Trying to get the HMAC validation working for incoming Cognigy.AI webhooks. The docs mention a max timestamp drift limit, but the Python script keeps getting rejected.
Ran this locally. The sig matches when I check manually, but it’s throwing a 401. Suspect the timestamp check is too tight. The webhook ID reference in the header isn’t clear either.
import hmac
import hashlib
secret = "my_webhook_secret"
body = request.get_data()
sig_header = request.headers.get('X-Cognigy-Signature')
ts = request.headers.get('X-Cognigy-Timestamp')
expected = hmac.new(secret.encode(), f"{ts}{body}".encode(), hashlib.sha256).hexdigest()
if not hmac.compare_digest(expected, sig_header):
return "Bad sig", 401
The X-Cognigy-Signature format looks like sha256=.... Is the timestamp supposed to be part of the payload string for the hash? Also, how do I handle the nonce validation? The request drops if the timestamp is more than 60 seconds off. Server clock is drifting. hmac.compare_digest returns false every time. IP allowlist is set, so that’s not it. Just getting auth failures on the atomic POST receive.
import time
import hmac
import hashlib
from fastapi import Request, HTTPException
MAX_DRIFT_SECONDS = 30
async def verify_cognigy_signature(request: Request, secret: str) -> bool:
body = await request.body()
signature = request.headers.get("x-cognigy-signature")
timestamp = request.headers.get("x-cognigy-timestamp")
if not signature or not timestamp:
raise HTTPException(status_code=401, detail="Missing auth headers")
current_time = int(time.time())
if abs(current_time - int(timestamp)) > MAX_DRIFT_SECONDS:
raise HTTPException(status_code=401, detail="Timestamp drift exceeded")
mac = hmac.new(secret.encode(), body, hashlib.sha256)
computed_sig = mac.hexdigest()
if not hmac.compare_digest(computed_sig, signature):
raise HTTPException(status_code=401, detail="Signature mismatch")
return True
Problem
Timestamp drift kills these integrations. You’re comparing the header time against local server time with zero buffer. The Cognigy platform sends the timestamp in UTC, and if your server clock is even two seconds off, or if network latency hits, you get rejected. This drift issue shows up when GC triggers the webhook via /api/v2/flows/actions too. The webhook ID isn’t in the header either. It lives in the JSON payload under the request object.
Code
The snippet above handles the drift check. Bumping the margin to 30 seconds works better. FastAPI makes this clean with request.body(). You need to hash the raw bytes, not a string representation. hmac.compare_digest is mandatory to stop timing attacks. Wrapping this in a middleware class keeps the route handlers clean. Found this pattern after a few late nights debugging proxy timeouts.
Error
Skipping the drift check opens up replay attacks. Enforcing it too strictly generates 401s on valid requests. The signature mismatch error usually means hashing the wrong body format. Some clients send application/json, others send form data. The hash must match the exact bytes received.
Question
Clock sync matters. Check NTP settings on the load balancer. Drift accumulates faster than expected.
Clock sync is always a pain. We hit this exact timestamp drift wall when wiring Cognigy callbacks into our CXone Studio flows, and the EC2 instance was running forty seconds behind. Tried bumping the drift constant to sixty seconds, which just pushed the 401 errors into the afternoon batch. Swapped to UTC normalization, but the HMAC comparison still choked on byte encoding differences. The real gotcha here is that the webhook secret needs to be URL-encoded before signing, otherwise the hash mismatch will keep triggering even when your clock is perfectly aligned. How are you handling the secret encoding on the receiving end?
Here is the corrected validation block that actually passes the signature check. We dropped the manual time math and let the standard library handle the drift window while forcing UTF-8 encoding on both sides.
import hmac
import hashlib
import time
from urllib.parse import quote
MAX_DRIFT = 30
secret = quote("my_webhook_secret", safe="")
body = await request.body()
timestamp = int(request.headers.get("x-cognigy-timestamp", 0))
signature = request.headers.get("x-cognigy-signature", "")
if abs(time.time() - timestamp) > MAX_DRIFT:
raise HTTPException(status_code=401, detail="Timestamp drift exceeded")
expected_sig = hmac.new(secret.encode("utf-8"), body, hashlib.sha256).hexdigest()
if not hmac.compare_digest(expected_sig, signature):
raise HTTPException(status_code=401, detail="Invalid signature")
Coming from Five9, I didn’t realize CXone’s token rotation would mask this kind of clock skew. It’s easy to miss. The /api/v2/oauth2/token endpoint auto-handles drift for PureCloudPlatformClientV2 sessions using the oauth:session:write scope, but raw scripts don’t get that safety net.
Tested the standard drift bump. Failed during peak queue times. Don’t widen that window past sixty seconds. Replay attacks will hit the analytics ingestion endpoint hard. What exact timestamp format is Cognigy pushing? Epoch or ISO? The parser chokes on milliseconds.
Tried the drift bump on the .NET backend service running the reporting dashboard. It choked on the byte array conversion just like the Python script. Ran a quick test hitting /api/v2/users/me to check the server clock latency against the platform time. The response headers show the timestamp is off by forty seconds on the Seoul region instance. Also tried hitting /api/v2/telephony/phone-lines to verify network latency. Same result.
Bumping the drift constant past sixty seconds feels risky for the analytics ingestion. Swapped to a strict UTC check instead. The HMAC comparison needs the secret encoded as UTF-8 before hashing. The docs imply binary encoding, which breaks the signature. Also tried using the webhook:write scope to force a refresh, but the token validation still timed out. Wasted half a day chasing scope permissions when it was just the encoding. The dashboard backend keeps flagging the webhook as unverified. Does the SDK handle the UTF-8 encoding automatically or is that manual? Here’s the C# implementation that finally passed the validation:
var secretBytes = Encoding.UTF8.GetBytes("my_webhook_secret");
using (var hmac = new HMACSHA256(secretBytes))
{
var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(body));
var computedSig = BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
}
The signature still fails if the body contains double-encoded JSON. The webhook payload looks like it’s stringified twice before the hash. Gotta check the serialization settings.