EventBridge Rule matches Genesys Cloud but Lambda returns 403

What’s the best way to handle the signature validation for Genesys Cloud webhooks when routing through AWS EventBridge to a Lambda consumer?

1. Created EventBridge partner event source for Genesys Cloud.
2. Set up Lambda function to process call.analysis.completed events.
3. Lambda returns 403 Forbidden on the initial handshake.

The X-Genesys-Signature header is present, but my Python handler fails to verify it against the shared secret. Is the payload structure different when coming through EventBridge versus direct HTTP?

If you check the docs, they mention that signature verification must occur before any business logic, but the handshake failure suggests a mismatch in the HMAC algorithm or the payload encoding. You are likely computing the hash on the raw body string instead of the UTF-8 encoded bytes, or vice versa, depending on how your Lambda parses the event.

For security audit pipelines, I always enforce strict OAuth 2.0 validation alongside the webhook signature to prevent replay attacks. Here is the corrected approach for your Python handler:

1. Extract the X-Genesys-Signature header.
2. Extract the X-Genesys-Delivery-Id to prevent duplicates.
3. Compute the HMAC-SHA256 hash of the raw request body using your shared secret.
4. Compare the computed hash with the header value using hmac.compare_digest.

The issue often stems from how boto3 or your framework encodes the event['body']. Ensure you are hashing the exact byte sequence received.

Here is the corrected verification logic and the expected payload structure:

{
 "version": "0",
 "id": "unique-event-id",
 "detail-type": "call.analysis.completed",
 "source": "genesys.cloud",
 "account": "123456789012",
 "time": "2023-10-27T10:00:00Z",
 "region": "us-east-1",
 "resources": [],
 "detail": {
 "interactionId": "abc-123",
 "transcript": "Customer called about billing...",
 "sentiment": "negative"
 }
}

Use this Python snippet to verify the signature correctly:

import hmac
import hashlib
import json

def verify_signature(body_bytes: bytes, signature: str, secret: str) -> bool:
 mac = hmac.new(secret.encode('utf-8'), body_bytes, hashlib.sha256)
 computed_sig = mac.hexdigest()
 return hmac.compare_digest(computed_sig, signature)

Ensure your Lambda returns 200 OK immediately after verification, even if processing fails asynchronously, to stop EventBridge retries. This prevents the 403 Forbidden loop you are experiencing.