title: Creating session from referrer
body: <p><strong>Background:</strong> I have a website, which we'll call AwesomeSite.com; it handles all of my traffic. Additionally, for the purposes of marketing I have a second domain, which we'll call PromoForAwesomeSite.com; it redirects all traffic straight to AwesomeSite. Both sites are built using PHP, MySQL, and Apache.</p>
  
  <p><strong>Problem</strong>: I want to serve up different content to users based on how they came to my site. Specifically, I want to show promos if the user was redirected from PromoForAwesomeSite.</p>
  
  <p><strong>Question:</strong> How can I detect that a user came from PromoForAwesomeSite and thus create a different session state for them?</p>
  
  <p><em>p.s. I am well aware of the shortcomings of this approach, in that once a session cookie is deleted promo users cannot see the promo content unless they revisit the redirect site (not likely). Unfortunately, this cannot be helped.</em></p>