Check timestamp from URI param string

I’m used to the HA-Proxy but new to Lua … and what I am trying to do is about to get information from requested URI and check with Lua if, for example, the timestamp provided is within last 30 minutes or more (expired) and so on … with some kind of bool return.
As a second example, I’ve been looking for decoding another string provided in request string to make sure it is ‘hashed’ from a common value + path with the backend who generated the link (no matter how).

I’ve been looking for two days and cannot find that kind of “simple” checks.
I’ve also been trying with functions like

if (math.abs(tonumber(ts) - tonumber(curr_ts)) <= delta) then
    return true
return false

but I could not manage to get any results … is it possible to get some help to know if it is possible and where’s the direction I should go?

Thanks a lot!