Amazon SNS notification validation when RawMessageDelivery is enabled

How do I validate an SNS notification when RawMessageDelivery is true? It doesn't contain the Signature, the SignatureVersion or the SigningCertURL.

These are all the headers I receive:

x-amz-sns-message-type
x-amz-sns-message-id
x-amz-sns-topic-arn
x-amz-sns-subscription-arn
x-amz-sns-rawdelivery