How to delete session of The HTTP_USER_AGENT - php

Question

In order to increase the security for the logged-in users, after the session_start(); and assigning the other session variables, I also try to store the HTTP_USER_AGENT value, using $_SESSION['agent'] = md5($_SERVER['HTTP_USER_AGENT']); for the login.php page.
Besides, in the login.php page, I redirect logged-in users to the home page if they try to visit it again without logging it out first, using the conditional like this:
if (isset($_SESSION['agent']) OR ($_SESSION['agent'] = md5($_SERVER['HTTP_USER_AGENT']) ) ) {
//redirect to home page
header('location:http://index.php.com');
exit();
}
The question is that in my logout.php page I code the conditional like this:
if (!isset($_SESSION['agent']) OR ($_SESSION['agent'] != md5($_SERVER['HTTP_USER_AGENT']) ) ) {
//Redirect to home page
}else{
$_SESSION = array(); // Destroy the variables.
session_destroy(); // Destroy the session itself.
setcookie (session_name(), '', time()-3600); // Destroy the cookie.
}
Then I came back to visit the login.php page again as a logged-in user (session has been set), it still redirected me to the home page.
Then I tried deleting the cookies in the FF browser, close it, then revisited the login.php page, it still redirected me.
Do you know what I was wrong or missing?
NOTE: I have no problem to destroy the session if not storing **the HTTP_USER_AGENT

Answer 1

You have an assignment where you want to check.
Change:
if (isset($_SESSION['agent']) OR ($_SESSION['agent'] = md5($_SERVER['HTTP_USER_AGENT']) ) ) {
to
if (isset($_SESSION['agent']) OR ($_SESSION['agent'] == md5($_SERVER['HTTP_USER_AGENT']) ) ) {
off topic security tip(maybe helpfull):
public function Start_Secure_Session()
{
// Forces sessions to only use cookies.
ini_set('session.use_only_cookies', 1);
// Gets current cookies params
$cookieParams = session_get_cookie_params();
// Set Cookie Params
session_set_cookie_params($cookieParams["lifetime"], $cookieParams["path"], $cookieParams["domain"], $this->isHTTPS, $this- >deny_java_session_id);
// Sets the session name
session_name($this->session_name);
// Start the php session
session_start();
// If new session or expired, generate new id
if (!isset($_SESSION['new_session']))
{
$_SESSION['new_session'] = "true";
// regenerate the session, delete the old one.
session_regenerate_id(true);
}
}