What does a Vary header field listing request field names instruct a cache to do?
Skip caching the response, because it depends on request-specific input
Expand the cache key, so a stored response matches only requests with the same values for the listed fields✓Respuesta correcta
Store one response per listed field name and merge them when serving
Revalidate the response with the origin server on every subsequent request
Explicación
Vary widens the cache key rather than disabling caching; the response is still stored and reused, but only for requests whose listed fields match the original request. Vary: * is the form that always fails to match, and unconditional revalidation is what no-cache asks for.