#   Cache directives are
#     action=never-cache
#     action=ignore-no-cache          (client & server no cache)
#     action=ignore-client-no-cache   (only client no cache)
#     action=ignore-server-no-cache   (only server no cache)
#     pin-in-cache=<time>
#     revalidate=<time>
#     ttl-in-cache=<time>             (force caching and expire after <time>)