Авторизация через steam openID

Warning: Cannot modify header information - headers already sent by (output started at D:\OpenServer\OpenServer\domains\localhost\src\templates\site\header.php:53) in D:\OpenServer\OpenServer\domains\localhost\src\steamauth\steamauth.php on line 24

<?php
ob_start();
@session_start();
require ('openid.php');
 
function logoutbutton() {
    echo "<form action=\"steamauth/logout.php\" method=\"post\"><input value=\"Logout\" type=\"submit\" /></form>"; //logout button
}
 
function steamlogin()
{
try {
    require("settings.php");
    $openid = new LightOpenID($steamauth['domainname']);
    
    $button['small'] = "small";
    $button['large_no'] = "large_noborder";
    $button['large'] = "large_border";
    $button = $button[$steamauth['buttonstyle']];
    
    if(!$openid->mode) {
        if(isset($_GET['login'])) {
            $openid->identity = 'http://steamcommunity.com/openid';
            header('Location: ' . $openid->authUrl());
        }
    echo '<form action="?login" id="loginForm" method="post"> </form>';
}
 
     elseif($openid->mode == 'cancel') {
        echo 'User has canceled authentication!';
    } else {
        if($openid->validate()) { 
                $id = $openid->identity;
                $ptn = "/^http:\/\/steamcommunity\.com\/openid\/id\/(7[0-9]{15,25}+)$/";
                preg_match($ptn, $id, $matches);
              
                $_SESSION['steamid'] = $matches[1]; 
                 if (isset($steamauth['loginpage'])) {
                    header('Location: '.$steamauth['loginpage']);
                 }
        } else {
                echo "User is not logged in.\n";
        }
 
    }
} catch(ErrorException $e) {
    echo $e->getMessage();
}
}
 
?>

<?php
$steamauth['apikey'] = "56284DF6F00A85D3CFBD4C6E2496C515"; // Your Steam WebAPI-Key found at http://steamcommunity.com/dev/apikey
$steamauth['domainname'] = "localhost/src/"; // The main URL of your website displayed in the login page
$steamauth['buttonstyle'] = "small"; // Style of the login button [small|large_no|large]
$steamauth['logoutpage'] = "http://localhost/src/index.php"; // Page to redirect to after a successfull logout (from the directory the SteamAuth-folder is located in) - NO slash at the beginning!
$steamauth['loginpage'] = "http://localhost/src/index.php"; // Page to redirect to after a successfull login (from the directory the SteamAuth-folder is located in) - NO slash at the beginning!
// System stuff
if (empty($steamauth['apikey'])) {die("<div style='display: block; width: 100%; background-color: red; text-align: center;'>SteamAuth:<br>Please supply an API-Key!</div>");}
if (empty($steamauth['domainname'])) {$steamauth['domainname'] = "localhost";}
if ($steamauth['buttonstyle'] != "small" and $steamauth['buttonstyle'] != "large") {$steamauth['buttonstyle'] = "large_no";}
?>