In this article Martin explains how to create a secure PHP login script that will allow safe authentication. Features remember-me function using cookies, validates logins on each request to prevent session stealing.

How Does This Work

This is a short explanation why I have chosen these authentication methods.

Users with shell access to the web server can scan valid session id's if the default /tmp directory is used to store the session data.

The protection against this kind of attack is the IP check.

Somebody who has a site (on a shared host with you) can generate valid session for your site.

This is why the checkSession method is used and the session id is recorded in the database.

Somebody may sniff network traffic and catch the cookie.

The IP check should eliminate this problem too.

Preparation

You need first to decide what information to store about members, the examples provided will assume almost nothing to make it easier to read.

I will use the PHP 4.1 super global arrays like $_SESSION, $_GET, etc. If you want to make it work on an earlier version of PHP you will have to substitute these with $GLOBALS['HTTP_SESSION_VARS'].

Read More...