Q:

Constant Password Checking?

I have read on stackoverflow the following: 
never store the users password or even a hash of the password in session or cookie data. 

I'm in the middle of making a system to check for a constant password, if it's different from one saved in a session, then force a logout; something like facebook does? When you change your password, or a password has been changed, you get logged out.
My code follows below: 
function ConstantPassword($Password)
{
    if ($_SESSION['Password'] !== $Password)
    {
        include "Logout.php";
    }
}

But, If it's said not to store passwords in a session/cookie? What could be another workaround for this? 

A:

You can do the check once, and then store a $_SESSION['logged_in'] = TRUE variable. On logging out, you unset($_SESSION['logged_in']) it and session_destroy() the session. No need to put the password nor the salt in the session.
Also, you should not implement passwords on your own but instead, use this: https://github.com/ircmaxell/password_compat It's the library that's going to be in PHP 5.5.

