Webhooks and validate HMAC

[Chamara Samaranayake]

Hello,

I'm trying to execute an AWS Lambda function using the Bitbucket webhooks. I've generated a function url from the Lambda function and configured it as the URL for the webhook. Also setup a secret in the webhook. 

I can successfully execute the Lambda function when I do any code pushes to the repository. I am trying to validate the HMAC using the x-hub-signature header. I'm using Python in my Lambda function. Every time when I compare the hash values they are different. 

Below is what I'm trying in Python. 

def checkSignature(signingSecret, signature, event):
signatureHash = signature.split('=')[1]
digest = hmac.new(signatureHash.encode('utf-8'), json.dumps(event).encode(), hashlib.sha256).hexdigest()

return hmac.compare_digest(digest, signatureHash)

Any help on what I am doing wrong would be really appreciated. 

Thank you