Enhance Response cache-control header

I have been trying to use Open API to specify the expected Cache rules for some API routes

While defining such rules through the Expires and/or Pragma headers can be quite simple (a date for Expires & the no-cache constant for Pragma), they are not the modern way to do it. Pragma is deprecated, and Expires is ignored when Cache-Control is defined.

Cache-Control is also nowadays supported by all clients making it the most obvious solution to define the caching rules.

Unfortunately, the current OPEN API Header Object support looks a bit limited for Cache-Control. Using pure JSON Schema definition might produce unexpected behavior without dedicated context for this header or for headers having similar Design.

This header value is defined as a comma-seperated list of properties called directives
If all directives were simple strings I could write something like that if I allowed any of them (or restrict to the on I accept by design)

      responses:
        200:
          description: "The request was successfully treated."
          headers:
            Cache-Control: 
              schema:
                type: array
                items:
                  type: string
                  enum:
                  - public
                  - private
                  - no-cache
                  - no-store
                  - must-revalidate
                  - proxy-revalidate
                  - immutable
                  - no-transform
                  - only-if-cached

If I want my route to prevent response to be cached I can easily design it a more simple way

            Cache-Control: 
              schema:
                type: string
                enum:
                - no-store

Or with the last JSON-Schema edition support of constants

            Cache-Control: 
              schema:
                const: "no-store"

But some of the most important cache control properties are key value pairs like max-age=300

I tried to express it the most reiable still simple way using adavanced JSON Schema feature unfortunately not really well supported (yet?) by Open API implementations

Sample 1

• Pro:
  • shortest
• Cons:
  • forbid different property order
  • forbid potentially acceptable other cache-control properties
  • not really the most inspectable

            Cache-Control: 
              schema:
                const: "public, max-age=300"

Sample 2

• Pro:
  • still short
• Cons:
  • ⚠️❌ the specification doesn't say how to serialize the object

            Cache-Control: 
              schema:
                const: ["public", {"max-age": 300}]

Sample 3

• Pro:
  • explicit, no need for const support
• Cons:
  • very verbose
  • pretty sure enum not well supported for numbers
  • ⚠️❌ the specification still doesn't say how to serialize the object

            Cache-Control: 
              schema:
                type: array
                items:
                  allOf:
                  - type: string
                    enum:
                    - public
                  - type: object
                    properties:
                      max-age:
                        type: number
                        enum:
                        - 300
                      required:
                      - max-age

Start by reviewing the OpenAPI Header Object, JSON Schema support, and the Cache-Control examples in this issue. No repository files or tests are identified; done would require agreeing on and documenting a precise, interoperable way to represent comma-separated directives and key-value directives such as max-age.