Q:

How to log all headers in nginx?

How do I log all the headers the client (browser) has sent in Nginx? I also want to log the response headers. Note that I am using nginx as reverse proxy. 
After going through documentation, I understand that I can log a specific header, but I want to log all of the headers. 

A:

After much research, I can conclude that it is not possible out of the box. 
Update- you can use openresty which comes with Lua. Using Lua one can do pretty cool things, including logging all of the headers to say, Redis or some other server

A:

As @gauravphoenix said you need opnresty which comes with Lua.  See https://github.com/openresty/lua-nginx-module/ for installing it.  Once it's running then add in nginx
header_filter_by_lua_block {
  local h = ngx.req.get_headers()
  for k, v in pairs(h) do
    ngx.log(ngx.ERR, "Got header "..k..": "..v..";")
  end
}

Inspect your error log.

A:

Based on @user1778602 response the set_by_lua can be used to set all headers into a variable to be consumed later at the log_format. The following sets all headers in the variable "$request_headers"
set_by_lua $request_headers '
  local h = ngx.req.get_headers()
  local request_headers_all = ""
  for k, v in pairs(h) do
    request_headers_all = request_headers_all .. ""..k..": "..v..";"
  end
  return request_headers_all
';

