How do you stop double logging in using PHP and MySQL?

Answer 1

Assuming you are using a User database and sessions, simply add a Session key. Auto generate this key as follows:

$newsession_key = SHA1( RAND(100000000,999999999));

Enter this in the database on the user row when logging in and store it in a session and in the database. Then on your code where you define the user logged in status you add something like:

$database_session = $DATABASE['sessionkey'];

If($database_session != $_SESSION['sessionkey']){

Unset($_SESSION['username'],$_SESSION['password'],$_SESSION['sessionkey']); #A*

}

A* Add in any sessions you use to keep the user logged in.