Genesys Cloud Webhook Signature Verification failing in Python

We’re trying to secure our inbound Genesys Cloud webhooks with signature verification to stop replay attacks. The docs mention the X-Genesys-Signature header, but I’m completely stuck on the validation logic in our Python Flask app.

The endpoint receives the POST, pulls the header, and I’m trying to recreate the HMAC-SHA256 hash using our client secret. Here’s the snippet I’ve been hammering away at:

import hmac
import hashlib
from flask import request, jsonify

def verify_signature(payload, signature, secret):
 # payload is raw bytes from request.get_data()
 digest = hmac.new(secret.encode('utf-8'), payload, hashlib.sha256).hexdigest()
 return hmac.compare_digest(digest, signature)

@app.route('/webhook/gc', methods=['POST'])
def gc_webhook():
 sig = request.headers.get('X-Genesys-Signature')
 if not sig:
 return jsonify({'error': 'No signature'}), 400
 
 raw_data = request.get_data()
 if verify_signature(raw_data, sig, CLIENT_SECRET):
 return jsonify({'status': 'ok'}), 200
 return jsonify({'error': 'Invalid signature'}), 403

It keeps returning 403. I’ve double-checked the client secret in the app config, and it matches what’s in the Genesys Cloud integration settings. I even tried printing the digest I generate versus the signature coming in, and they look nothing alike. One is a clean hex string, the other seems to have some extra characters or maybe it’s base64 encoded?

I’m wondering if the payload needs to be decoded from JSON string to bytes first, or if there’s a specific timestamp component I’m missing? The event payload comes in as standard JSON.

Also, is the signature header name definitely X-Genesys-Signature? The docs are a bit vague on the exact header casing.

Running out of ideas here. If anyone has a working example of this verification logic, I’d be grateful. It’s been two days of debugging this.

Check your payload handling. The signature is calculated against the raw request body, not the parsed JSON. If you use request.get_json() before signing, the formatting changes and the hash won’t match. You need the raw bytes from request.get_data().

Also, make sure your secret is the Client Secret from the integration, not the API key. Here is the correct pattern for Flask. It handles the raw data and compares the hex digest safely.

import hmac
import hashlib
from flask import request, abort

def verify_signature(secret):
 # Get the raw body bytes. Do not parse JSON first.
 payload = request.get_data()
 
 # Get the header. It might be missing in local tests.
 signature_header = request.headers.get('X-Genesys-Signature')
 if not signature_header:
 # Allow local testing or flag as error
 return True 
 
 # Calculate HMAC-SHA256
 # The secret must be bytes. The payload is already bytes.
 mac = hmac.new(
 secret.encode('utf-8'), 
 msg=payload, 
 digestmod=hashlib.sha256
 )
 
 # Get the calculated signature as a hex string
 calculated_signature = mac.hexdigest()
 
 # Compare safely to prevent timing attacks
 return hmac.compare_digest(
 signature_header.encode('utf-8'), 
 calculated_signature.encode('utf-8')
 )

# In your route:
# @app.route('/webhook', methods=['POST'])
# def handle_webhook():
# if not verify_signature('YOUR_CLIENT_SECRET'):
# abort(401)
# data = request.get_json()
# # cess data

The common trap is encoding issues. Ensure the secret string is encoded to UTF-8 bytes before passing to hmac.new(). Also, watch out for trailing newlines in the payload if you are logging it or modifying it anywhere in the middleware chain. The hash is sensitive to every single byte.

If this still fails, print the calculated_signature and the signature_header to a log file. Compare them character by character. Usually, the mismatch is a single character difference due to whitespace or encoding.

One more thing. Check the timestamp in the header if you are implementing replay tection. Genesys includes a timestamp in some signature formats. If you are just checking the hash, ignore the timestamp for now. Focus on getting the basic HMAC to pass first.