I'm using the nginx X-Accel-Redirect feature where a proxied backend (A) can "internally redirect" nginx to reprocess a new URI (B) as if that were the one originally given by the client browser.
It works great in making request B (also proxied)and returning B's resulting headers back to the client browser. So far so good.
But also I have some headers from A which I'd like to pass along too. In other words, merge a handful of headers from A in with the result from B.
How can I do this? I've tried
add_header X-My-Header $http_x_my_header;
$http_x_my_header variable is empty, presumably because the original request didn't have it. I've also tried
$upstream_x_my_header but that's empty too. I've tried things like
proxy_pass_header X-My-Header; but no.