Marketing Cloud Event Notification Service signs every notification delivered to your callback with an HMAC-SHA256 signature. The signature is produced by signing the entire notification payload using a signature key unique to the callback.
Because the signature is a hash of the payload, the x-sfmc-ens-signature will be different with each request.
You receive the signature key when you create the callback.
You can retrieve a callback’s signature key only during callback creation. Be sure to save the signature key for future use.
The x-sfmc-ens-signature arrives base64 encoded. The signature must first be decoded to provide the actual HMAC-SHA265 hash.
Here's a Java pseudo-code example of decoding:
To validate the authenticity of a notification, use the callback signature key to create an HMAC-SHA256 signature of the notification payload received. Then compare the HMAC-SHA256 signature to the value in
x-sfmc-ens-signature. If the values match, you know that the source of the notification is Marketing Cloud.