match previous url to give alternate 'cancel' button - php

Question

I have a site with a normal admin and a super admin, both share some functions. A new function I am introducing is a admin serial activation. This is already implemented in normal admin and now I am trying to add same code to super-admin. If you are in normal admin or super admin you would click the serial to activate and move on to activate2.php to activate. All works well and good unless you change your mind about activating serial, in which case you would click 'back' or a 'cancel' button to return to previous screen. I currently check what the previous page was using php:
$ref = $_SERVER['HTTP_REFERER'];
The idea is to show a different return url on 'back' link and the 'cancel' button depending on if the previous page was 'super-admin-serials.php' or just 'admin-serials.php'. I tried to match 'super-admin-serials.php' in $_SERVER['HTTP_REFERER'] to deduce what the previous page was and allow the user to go back to his previous page. But the code I have put together does not work, so if anyone out there can help with this simple function it would be much appreciated. Here is the code I have so far on the independent 'activate2.php' page to cancel and return to previous:
$superpage=array('super-admin-serials.php');
$ref = $_SERVER['HTTP_REFERER'];
if (in_array($ref, $superpage)) {
echo "back (super admin)";
} else {
echo "back (normal admin)" ;
}

Answer 1

The HTTP referer may not just contain the name of the script it comes to, it usually includes a fully qualified URL such as http://example.com/foo/your-script.php.
Instead of observing the HTTP referer (which will be lost if they refresh the page), I suggest that you pass an argument from the first page to the second to determine where they came from, and send them back where you need.
Transparently the user will be accessing either of:
activate2.php?super=1
activate2.php
Then the following code will do what you want:
$isSuper = !empty($_GET['super']);
if ($isSuper) {
echo "back (super admin)";
} else {
echo "back (normal admin)" ;
}

Answer 2

I understand you have some kind of sign in feature and you cannot be logged in simultaneously with two different users (if that's not the case, just make sure you aren't running an insecure site that can be easily hacked). In that case you should already have that information on the server so it's both unnecessary and unreliable to gather it from client-side. So code would look like this:
if ($_SESSION['is_super']) {
echo 'back (super admin)';
} else {
echo 'back (normal admin)';
}
(Please note I've also removed double quotes, which served no other purpose than making code harder to write and read.)
In any case, you must be aware that HTTP_REFERER:
Will get lost if you add extra steps (e.g. show form errors to get them corrected)
May not be there at all (some proxies and security programs strip it)
Will often include extra stuff that make a simple string comparison fail, like GET parameters (and it's of course a full URL)
If you opt for it anyway you may want to have a look at parse_url() as starting point.