Form token mismatch while using SimpleForm

Hi everyone,

I'm developing a custom luci web page for openwrt 19.07,

I want to redirect user to reset their default password after their first login.

So, I add an entry in network.lua

page = entry({"system", "login", "first"}, form("first"), _("Change Password"), nil)

some line in dispatcher.lua to redirect user to first.lua ,

which I refer to passwd.lua in luci-mod-admin-mini.

f = SimpleForm("password", translate("Admin Password"), translate("Change the password of the system administrator (User <code>root</code>)"))

pw1 = f:field(Value, "pw1", translate("Password"))
pw1.password = true
pw1.rmempty = false

pw2 = f:field(Value, "pw2", translate("Confirmation"))
pw2.password = true
pw2.rmempty = false

function pw2.validate(self, value, section)
	return pw1:formvalue(section) == value and value

function f.handle(self, state, data)
	if state == FORM_VALID then
		local state = luci.sys.user.setpasswd("root", data.pw1) == 0
		if state then
			f.message = translate("Password successfully changed")
			f.errmessage = translate("Unknown Error")
		data.pw1 = nil
		data.pw2 = nil
	return true

return f

The page display normally, but click submit button on this page will cause "Form token mismatch" error.

Can anyone help me find where I did wrong?