Hello,
I'm interested by your project since I have been using PHP for more than 8 years now. And this is the language you need to perform what you want.
What you want is pretty simple and it requires two things :
- the link you will post on the internet will be something like [login to view URL]
- you need to check if the variable a has the value 1 when the user reaches your website and store it in a session variable
- and finally when he makes a purchase, store this in a database or something
What can be complicated is to integrate this with your website, what are you using for your shopping cart ?
Best regards,
Laurent.