Creating session from referrer

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.

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.

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.