If a user logged in to my site with windows auth, how do I log the person out so that they will have to be authenticated again? (this is with IIS)

For example the user logs in like this:

Then the $_SERVER variable contains:

[REMOTE_ADDR] => 172.34.567.891
[REMOTE_HOST] => 172.34.567.891
[REMOTE_PORT] => 44601
[REMOTE_USER] => DOMAIN\username

And the user is not asked again for his username or password with windows auth unless the computer is restarted, or he uses a different browser.

How do I force the user to be authenticated again with PHP?

Update:

I found a way to do this, but it only works in chrome (all other browsers just throw a 401 unauthorized, even if the login is correct):

My code:

logout.php

    //clear session
    //then:
    $user = isset($_SESSION['userName']);
    $userNotSet = (!$user || (is_array($user) && count($user) == 0));


    if(!isset($_SESSION['401']) && $userNotSet) {
        $_SESSION['401'] = true;
        $realm = 'mysite';
        header('HTTP/1.1 401 Unauthorized');
        header('WWW-Authenticate: Digest realm="'.$realm.
           '",qop="auth",nonce="'.uniqid().'",opaque="'.md5($realm).'"');
        exit;
    }
    elseif($userNotSet) {
        header('HTTP/1.1 401 Unauthorized');
        list($domain, $user) = explode("\\", $_SERVER['REMOTE_USER']);
        $_SESSION['userName'] = $user;
        $_SESSION['LoggedIn'] = true;
    }
    else    {
        header('Location: '.WEBROOT.INDEX);
    }
    exit;

Why doesn't this work in any other browser aside from Chrome? Is there a cross-browser solution?

• php
• windows
• iis-7
• windows-authentication

If you are using PHP with HTTP Basic Auth, then there are two $_SERVER variables you need to be using and testing: $_SERVER['PHP_AUTH_USER'] & $_SERVER['PHP_AUTH_PW'].

To force the display of the browser's HTTP basic auth login dialog, you send a 401 header. It doesn't matter if the user is logged in or not, you can send the 401 header at any time to force the user to re-enter their credentials.

This code shows the basics:

<?php

// If the force_login request variable exists, then we want the user to
// re-enter their login details.
if (isset($_GET['force_login']) && $_GET['force_login'] == 1) {
    header('WWW-Authenticate: Basic realm="realm"'); 
    header('HTTP/1.0 401 Unauthorized'); 
    exit;
}

// Login process
if (!$_SERVER['PHP_AUTH_USER']) {
    // The browser has not supplied $_SERVER['PHP_AUTH_USER'], so we need 
    // the user to log in 
    header('WWW-Authenticate: Basic realm="realm"'); 
    header('HTTP/1.0 401 Unauthorized'); 
    exit;

} else {
    // Test that the username/password combination are correct
    $expectedUsername = 'test';
    $expectedPassword = '1234';
    if ($_SERVER['PHP_AUTH_USER'] != $expectedUsername 
            && $_SERVER['PHP_AUTH_PW'] != $expectedPassword ) { 
        // not valid username/password - try again!
        header('WWW-Authenticate: Basic realm="realm"'); 
        header('HTTP/1.0 401 Unauthorized'); 
        exit;
    }
} 
// End login process


// The user is logged in here. we can display the page content
echo '<a href="?force_login=1">Force login</a>';

(As a side note, if you're using HTTP basic auth, ensure you're using SSL too!)