[SR-Users] Where do I place the logic for modifying auth and call requests?

Hello everyone. Some of my confusion probably comes from me coming from the web development world and not software dev, but I would greatly appreciate any response to the following question: I use the MySQL auth for my subscribers which is working great. However, let's say that I add the column "valid_until" in the subscriber table and want to check if today's date is less than the caller's valid_until value. I can set up the sqlops module without a problem and get the actual value, but I have no idea where I place the logic to compare it to a date and then pass on the OK message to Kamailio to continue the request. Is this done with embedded scripts? Or right there in the config file? Where can I find a list of what parts of the call request are exposed for customization from Kamailio? I'd greatly prefer to do things in Python or JavaScript, if that matters. Many thanks in advance! Erik Eklund