PHP login implements remember me function

How to implement the remember me function in PHP login? This article mainly introduces the implementation methods and security practices of PHP permanent login and remember me functions. This article focuses on using the database to implement more secure permanent login and remember me functions. I hope to be helpful.

Persistent login refers to a mechanism for continuous authentication 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 my observation, 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.

But 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:

<?php
$token = md5(uniqid(rand(), TRUE));
?>

You can save it in the user's session to associate it with a specific Users are associated, but this doesn't help you stay logged in across multiple sessions, which is a major premise. 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 verification program confirm which user ID 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).

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.

<?php
$salt = &#39;SHIFLETT&#39;;
$identifier = md5($salt . md5($username . $salt));
$token = md5(uniqid(rand(), TRUE));
$timeout = time() + 60 * 60 * 24 * 7;
setcookie(&#39;auth&#39;, "$identifier:$token", $timeout);
?>

When a user uses a persistent login cookie, you can check if it meets several criteria:

<?php

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

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

$now = time();
$salt = &#39;SHIFLETT&#39;;

list($identifier, $token) = explode(&#39;:&#39;, $_COOKIE[&#39;auth&#39;]);

if (ctype_alnum($identifier) && ctype_alnum($token))
{
  $clean[&#39;identifier&#39;] = $identifier;
  $clean[&#39;token&#39;] = $token;
}
else
{
  /* ... */
}

$mysql[&#39;identifier&#39;] = mysql_real_escape_string($clean[&#39;identifier&#39;]);

$sql = "SELECT username, token, timeout
        FROM   users
        WHERE  identifier = &#39;{$mysql[&#39;identifier&#39;]}&#39;";

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

    if ($clean[&#39;token&#39;] != $record[&#39;token&#39;])
    {
      /* Failed Login (wrong token) */
    }
    elseif ($now > $record[&#39;timeout&#39;])
    {
      /* Failed Login (timeout) */
    }
    elseif ($clean[&#39;identifier&#39;] !=
            md5($salt . md5($record[&#39;username&#39;] . $salt)))
    {
      /* Failed Login (invalid identifier) */
    }
    else
    {
      /* Successful Login */
    }

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

?>

You should insist on it Limit the use of permanent login cookies from three aspects.

1.Cookies need to expire within one week (or less)
2.Cookies should only be used for one verification (delete or regenerate after a successful verification)
3. Limit cookie expiration on the server side within a week (or less)

If you want the user to be remembered indefinitely, then as long as the user visits your application more frequently than the expiration time If it is large, simply regenerate the identifier and set a new cookie after each verification.

Another useful principle is to require users to provide a password before performing sensitive operations. You should only allow permanently logged-in users to access features of your app that are not particularly sensitive. Asking users to manually verify before performing some sensitive operations is an irreplaceable step.

Finally, you need to confirm that the user who logged out of the system is actually logged out, which includes deleting the permanent login cookie:

<?php
setcookie(&#39;auth&#39;, &#39;DELETED!&#39;, time());
?>

In the above example, the cookie is useless The value is populated and set to expire immediately. This way, even if a user's clock remains inaccurate and the cookie remains valid, he or she is effectively logged out.

Related recommendations:

Advanced PHP Tutorial: PHP Cookies

PHP Cookies are often used to identify users

Examples showing the use and verification of php token

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