> Note though, that by changing headers_in structure you are
> responsible for it's consistency. It's usually much better idea
> to use upstream functionality to create needed request to an
> upstream instead (proxy_set_body, proxy_pass_headers and so on).
>

but can i wait for the upstream to return and delay the request from passing on to backend as i do in my subrequest ?
when i use your suggested proxy directives i have no control on that

Gad