health check URI type rest (json)

Good afternoon.
I currently have a server configured with balancing via / locale and / upstream.
In / upstream I have a file declared for each backend group and in / locale my referenced operations groups.
It works perfectly but what I don't get is to do a "health check" at the "uri" level because the services I'm balancing are of the "rest" type. In the docu it only allows (or I have only found) to do a GET when what I want to do a POST adding my data afterwards.


Another thing that I can't do is get the "add_header" directive to work so that the server that attended the request is sent in the header

BestRegards