php如何判斷正常訪問和外部訪問

<?php  
session_start();  
if(isset($_POST['check'])&&!empty($_POST['name'])){  
    if($_POST['check'] == $_SESSION['check']){  
        echo "正常訪問";  
    }else{  
        echo "外部訪問";  
    }  
}  
    $token = md5(uniqid(rand(),true));  
    $_SESSION['check'] = $token;  
?>  
<form method="post" action="">  
<input type="text" name="name" />  
<input type="text" name="check" value="<?=$token;?>">  
<input type="submit">

URL：http://www.bianceng.cn/webkf/PHP/201410/45949.htm