How to transparently proxy to upstream?

Hi there,

I created a similat question once, but was not clear!

Therefore my setup:
nginx 1.10.3-0ubuntu0.16.04.3

Backend server (any web server running SSL)

I am trying to get this URI: https://mynginx.domain.net/upstream
to reach the upstream on https://upstream.domain.net/

location /upstream/ {
proxy_pass https://upstream.domain.net:443/;
proxy_set_header Host $host;
}

This then makes a 302 and I see the direct upstream server.
Now imagine I want to expose just the proxy, how can I get all requests to the context forwarded to the upstream (and get handled properly)?

Thanks
David