reverse proxy through upstream proxy (1 reply)

I'm trying to configure nginx as a reverse proxy where the upstream traffic has to go through another proxy (squid in this case) without success. Since nginx does not support (as far as I can tell) passing a proxy for upstream and because I need to reverse proxy only one domain (test.com) I've tried rewriting the URL and using proxy pass:

location / {
rewrite ^ http://test.com$request_uri;
proxy_set_header X-Custom SOMETOKEN;
proxy_pass http://my_squid:3128;
}

Unfortunately since the final URL generated by rewrite starts with http nginx immediately returns a 302 without forwarding the request to the proxy.

Any ideas how to solve this or if there are alternative solutions to what I'm trying to achieve ?

Thanks.