Stuffing the entire aad into a single property prevents policies

[jakajancar]

See: https://docs.aws.amazon.com/kms/latest/developerguide/conditions-kms.html#conditions-kms-encryption-context

The key provider trait should maybe take HashMap<String, String> instead.

[coderdan]

Thanks for submitting this @jakajancar and apologies for the slow reply. What you suggested makes sense. We'll work add it to our queue.