仅允许来自特定网址的请求

Question

I've made a CSS template which I can sell. The css is hosted on my server. I only want site's who paid to have access to this file, so I thought of a php file which echo's the css, only if the url exists in an array.

<?php

header("Content-type: text/css");

$allowedUrls = ['google.com', 'facebook.com'];

$thisURL = "http://urlfromrequester.com"; //???
$thisURL = str_ireplace('www.', '', $thisURL);
$thisURL = (parse_url($thisURL, PHP_URL_HOST));

foreach ($allowedUrls as $url) {
    if ($url == $thisURL) {
        $css = file_get_contents('theCSSFile.css');
    } else {
        $css = file_get_contents('FileWithLinkToBuyPage.css');
    }
}

echo($css);

This is a safe way to only print the css when the host bought the css file. But how can I get the URL of the requester?

People who buy this file will use it like this: <link rel="stylesheet" type="text/css" href="http://domain.com/checkLicence.php">

Thanks

Answer 1

You can use:

$_SERVER['HTTP_REFERER'];

Take into consider though, that the referral address is set by the user agent. Not all user agents will set this, and some provide the ability to modify HTTP_REFERER as a feature. In short, it cannot really be trusted.