Implementing Cross-Domain Cookies Page 2

Step 1: Setting Up A Prepend Script

Add the following code to a prepend script (or a function that appears at the top
of all scripts).

<?php
/* Support cross-domain cookies... */
// If the GET variable has been set, and it differs from the cookie
// variable, then use the get variable (and update the cookie) 
global $HTTP_COOKIE_VARS, $HTTP_GET_VARS; 
if (isset($sessionid) && isset($HTTP_GET_VARS['sessionid']) && ($HTTP_COOKIE_VARS['sessionid'] != $HTTP_GET_VARS['sessionid'])) { 
    SetCookie('sessionid', $HTTP_GET_VARS['sessionid'], 0, '/', ''); 
    $HTTP_COOKIE_VARS['sessionid'] = $HTTP_GET_VARS['sessionid']; 
    $sessionid = $HTTP_GET_VARS['sessionid'];
} 
?>

Once this code has been run, a global variable 'sessionid' will be available
to the script. It will contain the value of the sessionid from the users
cookie, or the value sent along with a GET request.

Step 2: Using Variables For All Cross-Domain Hrefs

Create a global configuration file that contains the base hrefs of the domains
you are switching between. For example, if we have domain1.com and domain2.com, set
the following:

<?php
$domains['domain1'] = "http://www.domain1.com/-$sessionid-";
$domains['domain2'] = "http://www.domain2.com/-$sessionid-";
?>

Now, if you do the following in your code…

<?php
echo "Click &lt;a href="", $domains['domain2'], "/contact/?email=yes"&gt;here&lt;/a&gt; to contact us.";
?>

…you will produce the following output…

Click <a href="http://www.domain2.com/-66543afe6543asdf6asd-/contact/?email=yes">here</a> to contact us.

…where the sessionid has been inserted into the URL.

At this point, you are probably thinking “this will try to open a subdirectory on
the webserver called dash, sessionid, dash?!?!?”. However, the next step will provide the necessary
magic to make it all work – mod_rewrite!