Example Steam OAuth with LightOpenID

<?php
# Logging in with Steam accounts requires setting special identity, so this example shows how to do it.
# http://steamcommunity.com/dev/
require 'openid.php';
try {
    # Change 'localhost' to your domain name.
    $openid = new LightOpenID('localhost');
    if(!$openid->mode) {
        if(isset($_GET['login'])) {
            $openid->identity = 'http://steamcommunity.com/openid';
            header('Location: ' . $openid->authUrl());
        }
?>
<form action="?login" method="post">
    <input type="image" src="http://cdn.steamcommunity.com/public/images/signinthroughsteam/sits_large_border.png">
</form>
<?php
    } elseif($openid->mode == 'cancel') {
        echo 'User has canceled authentication!';
    } else {
        if($openid->validate()) {
                $id = $openid->identity;
                // identity is something like: http://steamcommunity.com/openid/id/76561197994761333
                // we only care about the unique account ID at the end of the URL.
                $ptn = "/^http:\/\/steamcommunity\.com\/openid\/id\/(7[0-9]{15,25}+)$/";
                preg_match($ptn, $id, $matches);
                echo "User is logged in (steamID: $matches[1])\n";
        } else {
                echo "User is not logged in.\n";
        }

    }
} catch(ErrorException $e) {
    echo $e->getMessage();
}
?>