I have a website http://someplace.acme.com that I want my users to access via http://myplace.mycorp.com - pretty standard reverse proxy setup.

The special requirement: any js file - either identified by the .js extension and/or the mime-type (if that is possible) text/javascript needs to be served from a different location, a local tool that inspects the js for potential threats.

So I have

location / {
  proxy_pass  http://someplace.acme.com;
  proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
  proxy_redirect off;
  proxy_buffering off;
  proxy_set_header        Host            $host;
  proxy_set_header        X-Real-IP       $remote_addr;
  proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
}

location ~* \.(js)$ {
  proxy_pass http://127.0.0.1:8188/filter?source=$1;
  proxy_redirect off;
  proxy_buffering off;
}

The JS still is served from remote and I have no idea how to check for the mime type. What do I miss?