Enhanced header based cloaked site security enhancement

[kaerez]

Brief:
Allow server side loading of content with custom headers, not visible to the client side.

Details:
If a cloaked target, such as a form or anything else, needs to be a little more protected while maintaining the ease of use by non-dev's, if the target supports fetching a custom header then this would be configurable on Dub and then displayed to the user.
This would result in the target being unavailable/restricted if Dub is being bypassed.

A more advanced addition would be possible future support for adding a client side certificate but this may be serious overkill.

[linear]

ENG-443 Enhanced header based cloaked site security enhancement