How to send a request from Splash via proxy?

I am trying to make a SplashRequest to a page using such a script:

function main(splash, args)
  splash:on_request(function(request)
    request:set_proxy{'http://login:password@host_proxy_ip:port'}
  end)
  assert(splash:go(args.url))
  assert(splash:wait(0.5))
  assert(splash:set_viewport_full())
  return {
    html = splash:html(),
    url = splash:url(),
  }
end

The page returns without errors, but my real ip is specified, where is my error?

found a working option:

function main(splash, args)
          splash:on_request(function(request)
            request:set_proxy{
              host = "host_proxy_ip",
              port = port,
              username = "login",
              password = "password",
              type = "HTTP"
            }
          end
          )
          assert(splash:go(args.url))
          assert(splash:wait(0.5))
          assert(splash:set_viewport_full())
          return {
            html = splash:html(),
            url = splash:url(),
          }
        end