PHP permanent login, remember me function implementation methods and safety practices, PHP practices_PHP tutorial

PHP permanent login, remember me function implementation methods and security practices, PHP practices

Permanent login refers to the mechanism for continuous verification between browser sessions. In other words, a user who is logged in today will still be logged in tomorrow, even if user sessions expire between visits. The presence of persistent logins reduces the security of your authentication mechanism, but it increases usability. Instead of troublesome users to authenticate each time they visit, provide the option to remember the login.

From what I have observed, the most common flawed permanent login scheme is to save the username and password in a cookie. The temptation to do this is understandable - instead of prompting the user for a username and password, you can simply read them from the cookie. The rest of the verification process is exactly the same as a normal login, so this scenario is a simple one.

However, if you do store your username and password in cookies, please turn off this feature immediately and read the rest of this section to find some ideas for implementing a more secure solution. You will also need to require all users who use this cookie to change their passwords in the future because their authentication information has been exposed.

Permanent login requires a permanent login cookie, often called an authentication cookie, because cookies are the only standard mechanism used to provide stable data across multiple sessions. If the cookie provides permanent access, it poses a serious risk to the security of your application, so you need to make sure that the data you save in the cookie can only be used for authentication for a limited period of time.

The first step is to devise a method to mitigate the risk posed by captured persistent login cookies. While cookie capture is something you want to avoid, having a defense-in-depth process is best, especially since this mechanism can make your validation form less secure even when everything is working fine. In this way, the cookie cannot be generated based on any information that provides a permanent login, such as the user's password.

To avoid using the user's password, you can create an identity that is only valid for one-time verification:
Copy code The code is as follows:
$token = md5(uniqid(rand(), TRUE));
?>

You can save it in the user's session to associate it with a specific user, but that doesn't help you stay logged in across multiple sessions, which is a big deal. Therefore, you must use a different method to associate this identity with a specific user.

Since the username is less sensitive than the password, you can store it in a cookie, which can help the authenticator confirm which user's identity is provided. However, a better approach is to use a secondary identity that is difficult to guess and discover. Consider adding three fields to the data table that stores usernames and passwords: a second identity (identifier), a permanent login identification (token), and a permanent login timeout (timeout).
Copy code The code is as follows:
mysql> DESCRIBE users;
------------ ------------------ ------ ----- --------- -------
| Field | Type | Null | Key | Default | Extra |
------------ ------------------ ------ ----- --------- -------
| username | varchar(25) | | PRI | | |
| password | varchar(32) | YES | | NULL |
| identifier | varchar(32) | YES | MUL | NULL |
| token | varchar(32) | YES | | NULL |
| timeout | int(10) unsigned | YES | | NULL |
------------ ------------------ ------ ----- --------- -------

By generating and saving a secondary identity and permanent login ID, you can create a cookie that does not contain any user authentication information.
Copy code The code is as follows:

$salt = 'SHIFLETT';

$identifier = md5($salt . md5($username . $salt));
$token = md5(uniqid(rand(), TRUE));
$timeout = time() 60 * 60 * 24 * 7;

setcookie('auth', "$identifier:$token", $timeout);

?>

When a user uses a persistent login cookie, you can check if it meets several criteria:
Copy code The code is as follows:

/* mysql_connect() */
/* mysql_select_db() */

$clean = array();
$mysql = array();

$now = time();
$salt = 'SHIFLETT';

list($identifier, $token) = explode(':', $_COOKIE['auth']);

if (ctype_alnum($identifier) && ctype_alnum($token))
{
  $clean['identifier'] = $identifier;
  $clean['token'] = $token;
}
else
{
  /* ... */
}

$mysql['identifier'] = mysql_real_escape_string($clean['identifier']);

$sql = "SELECT username, token, timeout
        FROM   users
        WHERE  identifier = '{$mysql['identifier']}'";

if ($result = mysql_query($sql))
{
  if (mysql_num_rows($result))
  {
    $record = mysql_fetch_assoc($result);

    if ($clean['token'] != $record['token'])
    {
      /* Failed Login (wrong token) */
    }
    elseif ($now > $record['timeout'])
    {
      /* Failed Login (timeout) */
    }
    elseif ($clean['identifier'] !=
            md5($salt . md5($record['username'] . $salt)))
    {
      /* Failed Login (invalid identifier) */
    }
    else
    {
      /* Successful Login */
    }

  }
  else
  {
    /* Failed Login (invalid identifier) */
  }
}
else
{
  /* Error */
}

?>

你应该坚持从三个方面来限制永久登录cookie的使用。

1.Cookie需在一周内（或更少）过期
2.Cookie最好只能用于一次验证（在一次成功验证后即删除或重新生成）
3.在服务器端限定cookie在一周（或更少）时间内过期

如果你想要用户无限制的被记住，那只要是该用户的访问你的应用的频度比过期时间更大的话，简单地在每次验证后重新生成标识并设定一个新的cookie即可。

另一个有用的原则是在用户执行敏感操作前需要用户提供密码。你只能让永久登录用户访问你的应用中不是特别敏感的功能。在执行一些敏感操作前让用户手工进行验证是不可替代的步骤。

最后，你需要确认登出系统的用户是确实登出了，这包括删除永久登录cookie：
复制代码 代码如下:
setcookie('auth', 'DELETED!', time());
?>

上例中，cookie被无用的值填充并设为立即过期。这样，即使是由于一个用户的时钟不准而导致cookie保持有效的话，也能保证他有效地退出。

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