Transform Rules: Allow ability to set multiple dynamic headers of the same name

Following the addition of the Transform Rules - Response Header New Action “Add” feature, it’s now possible to add a new set-cookie header without clobbering existing set-cookie headers, which is nice.

But as noted in this comment, it’d be great to be able to add a new header with a dynamic value, matching the “Set Dynamic” option that is currently available.

An example concrete use-case:

  • Client wants to generate a unique device ID cookie at the edge.
  • Client wants to also generate an anti-CSRF token cookie with a dynamic value.

Both of these are separately possible today by creating a set-cookie header with Set Dynamic. But doing this will clobber all other set-cookie headers, including any of those set by Cloudflare itself (Bot Management cookie), and this case of setting two cookies is not possible.