nginx proxy authentication intercept

I have a couple of service and they stand behind an nginx instance. In order to handle authentication, in nginx, I am intercepting each request and sending it to the authentication service. There, if the credentials are are correct, I am setting a cookie which includes user related info.

The request should now be routed to the appropriate service, with the cookie set.

Here is my nginx config:

user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events {
  worker_connections  1024;
}

http {
  upstream xyz {
    server ***;
  }

  upstream auth {
    server ***;
  }

  server {
   listen       8080;
   location ~ ^/(abc|xyz)/api(/.*)?$ {
     auth_request /auth-proxy;

     set $query $2;

     proxy_pass http://$1/api$query$is_args$args;
     proxy_set_header X-Target $request_uri;
     proxy_set_header Host $http_host;
   }

   location = /auth-proxy {
    internal;
    proxy_pass http://auth;

    proxy_pass_request_body off;
    proxy_set_header Content-Length "";
    proxy_set_header X-Target $request_uri;
    proxy_set_header Host $http_host;
    proxy_set_header X-CookieName "auth";
    proxy_set_header Cookie "auth=$cookie_auth";
    proxy_set_header Set-Cookie "auth=$cookie_auth";
    proxy_cookie_path / "/; Secure; HttpOnly";
    add_header Cookie "auth=$cookie_auth";
    add_header Set-Cookie "auth=$cookie_auth";
  }
}

If I make a request to /auth-proxy with an x-target header set manually, the response contains the cookie as expected.

If I make a request to the desired target, the request is intercepted, it reaches /auth-proxy which correctly sets the cookie. However, when the request reaches the target, it does not contain the cookie.

I assume that nginx is not forwarding the cookie when doing the target request.

I've been struggling with this for the last couple of days... what am I missing?

Thanks!

I've finally figured it out. I used auth_request_set to read the cookie from the auth response and I manually set it both on the response to the caller and on the subsequent request to the target.

Because if is evil, I've added the check in lua.

server {
  listen       8080;
  location ~ ^/(abc|xyz)/api(/.*)?$ {
    auth_request /auth-proxy;

    # read the cookie from the auth response
    auth_request_set $cookie $upstream_cookie_auth;
    access_by_lua_block {
      if not (ngx.var.cookie == nil or ngx.var.cookie == '') then
        ngx.header['Set-Cookie'] = "auth=" .. ngx.var.cookie .. "; Path=/"
      end
    }
    # add the cookie to the target request
    proxy_set_header Cookie "auth=$cookie";

    set $query $2;

    proxy_pass http://$1/api$query$is_args$args;
    proxy_set_header X-Target $request_uri;
    proxy_set_header Host $http_host;
  }
}