FHIR Document Digital Signatures

I was asked about Digital Signatures for FHIR documents:I am working on _____  IG that is FHIR document based and we need a means to prove authenticity. The model is relatively simple in that a document and all of its parts represent a single thing that needs to be “signed”.I have looked around for examples of this in IGs and in example documents and I have not found anything. I see a lot of references to CDA documents and signatures,...