Code to generate the password

gistfile1.php

function user_login($username, $submitted) {

    /**
     * Retrieve the temporary/one-time password. While session-based is ok for
     *  this proof of concept, to make this more secure we'd want to use a database
     *  some sort of timeout to expire the password of N minutes/hours.
     */
    $stored = $_SESSION['password'];
    // Compare the retrieved vs the stored password
    if ($stored == $submitted) {
        $message = "Hello and welcome back $username";
    } else {
        $message = "Sorry, that's an invalid username and password combination.";
    }
    // Clean up after ourselves
    unset($_SESSION['username']);
    unset($_SESSION['password']);

    return $message;
}