Received error message in subject line whilst trying to use the Python ASK SDK.
Fixed the problem in file verifier_constant.py:
Changed SIGNATURE_HEADER = "Signature-256"
SIGNATURE_HEADER = "http_Signature_256"
SIGNATURE_CERT_CHAIN_URL_HEADER = "SignaturCertChainUrl"
SIGNATURE_CERT_CHAIN_URL_HEADER = "http_SignaturCertChainUrl"
Things work now. Seems like a bug to me. This might be helpful to others passing this way.