Hey folks,
We’re trying to lock down our EventBridge consumers by verifying the x-genesys-signature header. The docs say it’s a SHA256 HMAC, but our Python script keeps failing the check. Here’s the snippet we’re using:
import hmac
expected = hmac.new(secret.encode(), body.encode(), hashlib.sha256).hexdigest()
The signature always mismatches. Are we supposed to base64 decode the header first? Or is the body encoding different than UTF-8?
You’re running into a classic encoding mismatch here. The signature verification process is stricter than it initially appears.
The x-genesys-signature header isn’t just a plain hex string. It’s base64-encoded. But more importantly, the body you hash against must be the exact raw bytes received over the wire. If your Python framework (like Flask or FastAPI) has already parsed the JSON into a string or dictionary, you’ve lost the original whitespace and key ordering that Genesys used to generate the HMAC.
Here’s how I fixed it in a recent EventBridge setup. First, ensure you’re reading the raw body bytes. Second, decode the signature header from base64. Then compare.
import hmac
import hashlib
import base64
# 1. Get the raw body bytes (critical step)
raw_body = request.get_data()
# 2. Get the signature from the header
sig_header = request.headers.get('x-genesys-signature')
# 3. Base64 decode the signature
expected_sig = base64.b64decode(sig_header)
# 4. Calculate the HMAC using your shared secret
# Note: Use the same key used in Genesys Cloud webhook settings
secret_key = 'YOUR_SHARED_SECRET'.encode()
calculated_sig = hmac.new(secret_key, raw_body, hashlib.sha256).digest()
# 5. Compare securely
if not hmac.compare_digest(calculated_sig, expected_sig):
return "Invalid signature", 401
return "Success", 200
Don’t use hexdigest() on the calculated side if the header is base64. You need the raw digest bytes for comparison after decoding the header. Also, check that your webhook in Genesys Cloud is configured to send the signature. It’s not enabled by default for older webhooks. You might need to recreate the endpoint to pick up the new security settings.
The timezone doesn’t matter here, but the timestamp in the request body does if you’re validating freshness. Just stick to the raw body bytes.