How to detect users setting do-not-track

Question

I was looking through some Google articles and some Firefox developer areas and found that there was an option you can set to not let some sites track your information.

I looked into this and did some google searches for Developers and couldn't manage to find any information on how to detect whether or not a user has set this in their browser.

Is it sent in a POST request or in any type of request? Does it come in the User agent? I just wanted to know how to manage this and not store their ips for login as an example.

Answer 1

It's sent as an HTTP header:

function dnt_enabled()
{
   return (isset($_SERVER['HTTP_DNT']) && $_SERVER['HTTP_DNT'] == 1);
}

if dnt_enabled() {
    // do stuff...
}

Or, if you're using PHP 7:

function dnt_enabled(): bool
{
   return (bool)$_SERVER['HTTP_DNT'] ?? false;
}

Answer 2

$do_not_track_requested = ! empty( $_SERVER[ 'HTTP_DNT' ] );

All HTTP headers are present in $_SERVER, prefixed with HTTP_.

https://www.php.net/manual/en/reserved.variables.server.php#89567