title: Starting PHP session from email link
body: <p>I have an email containing links to various products that I have sent to potential clients.  When clicking on the link, I want to take the user to a page with a form on it.  Based on what product link they clicked, I want the value of a hidden input field to equal the product name.  </p>
  
  <p>I also want the page to only be accessible via the link in the email.</p>
  
  <p>How would I go about doing this?</p>