There is next to no documentation in the IG for this extension, making it very difficult to evaluate its efficacy and appropriate usage. 

The NDH Secure Exchange Artifacts extension carries a certificate and some metadata for it. But the use cases for when this extension would be needed are not documented; please do so. What does it mean to associate a certificate with an Endpoint? You don't need an SSL server cert, as you get that in the TLS handshake. You don't need a signing cert for SAML assertions or JWTs in messages, as those are typically carried in the signatures or made available via existing methods like this for SMART: https://hl7.org/fhir/uv/bulkdata/authorization/index.html#registering-a-smart-backend-service-communicating-public-keys.