Creating session from referrer - php

Question

Background: 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.
Problem: 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.
Question: How can I detect that a user came from PromoForAwesomeSite and thus create a different session state for them?
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.

Answer 1

You can utilize the $_SERVER['HTTP_REFERER'] and see if contains the PromoForAwesomeSite.com in the referrer string. For instance something like this:
session_start();
if(substr_count($_SERVER['HTTP_REFERER'] , 'PromoForAwesomeSite.com')){
$_SESSION['from_promo'] = 1;
}
As referrers can be blocked by the browsers, so you might look into the possibility of sending a GET param in the redirect string from the promo site. Not sure how you are redirecting from your promo site but if its PHP you can do something like this , if not you will get the idea what I mean :)
HEADER('Location: http://AwesomeSite.com/index.php?from=promo');
So instead of (or in additional to) checking the referrer you can also check for this string and save in the session.

Answer 2

In your case the referrer won't be carried on if you do an automatic redirect at the landing time. Thus, If I were you, I would handle it like this:
1. On PromoForAwesomeSite.com
header('Location: http://www.awesomesite.com/promo.php');
2. On AwesomeSite.com
a. Create a promo.php gateway page
b. On the gateway page
setcookie('Promo', '1', time()+(5 * (24 * 3600))); // five days promotion cookie - adjust it
header('Location: http://www.awesomesite.com/index.php');
c. On the index.php
if($_COOKIE['Promo']){
// show promotion
}
This way you will solve the issue with the session as well.