The NDH Dynamic Registration extension provides a critical value, which is identifying which trust mechanism is used (at this time, for FHIR it's UDAP or SMART). But it is misnamed and not documented. Dynamic registration is just one part of the OAuth 2 workflow, and it follows Discovery, where you either hit <FHIRBase>.well-known/smart-configuration or <FHIRBase>.well-known/udap. Is the field intended only to differentiate between OAuth 2 profiles? If so, then call it something like OAuth 2 Discovery. If it's broader, to include mechanisms like mTLS, then call it something like trust mechanism. Also, please document its meaning.