title: Read form POST variables with nginx
body: <p>I have a client program I cannot modify. It makes large POST (x-www-form-urlencoded) requests containing hundreds of variables across WAN links, but I only need 5 of them. I'm inserting nginx as a reverse proxy on the local client system. What's the easiest to get nginx to strip out the extra data?</p>
  
  <p>Two ways I see so far:
   1. Use Lua (If I did, should I do content_by_lua, rewrite the body, and then make a subrequest? Or is there a simpler way?)
   2. Use form-input-nginx-module and proxy_set_body to parse and grab a few variables out.</p>
  
  <p>I'm already using OpenResty, so Lua means no extra modules. But, it probably means writing more locations and so on to do subrequests.</p>