为什么即使php没有破坏它也没有显示按钮

<?php

require 'openid.php';
try 
{
    # Change 'localhost' to your domain name.
    $openid = new LightOpenID('localhost');

    if(!$openid->mode) 
    {

        if(isset($_GET['login'])) 
        {
            $openid->identity = 'https://www.google.com/accounts/o8/id';
            header('Location: ' . $openid->authUrl());
        }
?>

        <form action="?login" method="post">
            <button>Login with Google</button>
        </form>

<?php
    } 
    elseif($openid->mode == 'cancel') 
    {
        echo 'User has canceled authentication!';
    } 
    else 
    {
        echo 'User ' . ($openid->validate() ? $openid->identity . ' has ' : 'has not ') . 'logged in.';
    }
}        
catch(ErrorException $e) 
{
    echo $e->getMessage();
}

This question was asked but a big part wasn't answered due lack of testing , the question is that why doesn't the login with google button be shown after a login

note : this is openid and will be redirected to google after its shown and back to the page after logging to google but it doesn't show the button after the login, reason ?

for testing I have uploaded in http://dota2tradebots.com/googlelogin.php