I tried asking on the forum, but there were no replies. Asking here with slight modifications:

I am creating a POST endpoint where:

• Field A may or may not be required depending on the currently authenticated user
• Field B and C are required and D is optional, but that may change - in the future, only B may be required and not C, or D may be required
• Field E has an enumerated set of allowed values which may change

Is there a JSON:API-friendly way to communicate this to clients, so that the front-end knows which fields are required for POST, and which values to display in the drop-down for E?

One possible solution is to have a non-JSON:API (or at least not idiomatic) endpoint the client can query to get these constraints in some defined format. Are there better solutions?