Temporary resolution pending decision on #3:   HRex covers high-level aspects and points to SMART on FHIR framework and Bulk data = https://build.fhir.org/ig/HL7/davinci-ehrx/security.html#exchange-security and https://hl7.org/fhir/us/davinci-hrex/smart-app-reg.html Will remove the mention of the other efforts like FAST, DS4P etc. and other items we have on the that page, Reference HRex like done  in CDex here: http://build.fhir.org/ig/HL7/davinci-ecdx/security.html   Specific guidance for system level trust. (see  backend Services) between parties.  (see PDEX documentation here: http://build.fhir.org/ig/HL7/davinci-epdx/PayerToPayerExchange.html#future-direction-for-discovery-and-registration) . May leverage this as guidance.