nginx add_header not working

Question

I am having an intriguing problem where whenever I use add_header in my virtual host configuration on an ubuntu server running nginx with PHP and php-fpm it sim

Answer 1

Evidently the add_header inheritance quirk/gotcha applies to the upstream layer as well.

I had a script pre-authorizing requests meant for another service, and was therefore returning all of the headers from the other service.

Once I started adding an 'Access-Control-Allow-Origin' entry along with these relayed headers, the browser would actually get the entry and allow the request.