detect 409 from 3scale

nginx.lua

function error_authorization_failed(service)
  ngx.status = 409
  ngx.header.content_type = service.auth_failed_headers
  ngx.print("Limit exceeded")
  ngx.exit(ngx.HTTP_OK)
end

function authrep(params, service)
  ngx.var.cached_key = ngx.var.cached_key .. ":" .. ngx.var.usage
  local api_keys = ngx.shared.api_keys
  local is_known = api_keys:get(ngx.var.cached_key)

  if is_known ~= 200 then
     local res = ngx.location.capture("/threescale_authrep", { share_all_vars = true })

     if res.status ~= 200 then
      api_keys:delete(ngx.var.cached_key)
      ngx.status = res.status
      ngx.header.content_type = "application/json"
      -- return different response for 409 and 403
      if res.status == 409 then
        error_over_limit(service)
      else
        error_authorization_failed(service)
      end
      --
     else
        api_keys:set(ngx.var.cached_key,200)
     end
        ngx.var.cached_key = nil
  end
end