Rely on variable values, not only presense

[bobrik]

It it quite convenient to use map in nginx configuration. You can map tokens and secrets to hosts, but you cannot do the same with whitelists and boolean-ish variables. Current code only check for variable presence, you cannot explicitly disable things.

I suggest to add an extra check for currently problematic variables. Instead of

if whitelist then
 -- stuff
end

let's do

if whitelist and whitelist:len() > 0 then
  -- stuff
end

Setting ngo_secure_cookies to false should also work.