conntest-handler.lua

require('luci.util')
local nx_redir = false

function http_date(time)
	return os.date('!%a, %d %b %Y %H:%M:%S GMT', time)
end

function handle_request(env)
	local send = uhttpd.send
	if env.REQUEST_URI == '/' then -- NintendoWiFi
		if nx_redir then
			send('Status: 302 Found\r\n')
			send('Location: https://www.bing.com/\r\n\r\n')
		else
			local date = http_date(os.time())
			send('Status: 200 OK\r\n')
			send('Content-Length: 2\r\n')
			send('Expires: %s\r\n' % date)
			send('Cache-Control: max-age=0, no-cache, no-store\r\n')
			send('Pragma: no-cache\r\n')
			send('Date: %s\r\n' % date)
			send('X-Organization: Nintendo\r\n')
			send('Content-Type: text/plain\r\n\r\nok')
		end
	elseif env.REQUEST_URI == '/generate_204' then -- Android generate_204
		send('Status: 204 No Content\r\n')
		send('Date: %s\r\n\r\n' % http_date(os.time()))
	end
end

uhttpd

config uhttpd 'conntest'
	option rfc1918_filter '1'
	list listen_http '0.0.0.0:080'
	option home '/var/tmp'
	list lua_prefix '/=/root/conntest-handler.lua'
	option http_keepalive '0'
	option tcp_keepalive '0'

You need to run opkg install uhttpd-mod-lua first to install uHTTPd lua handler support.