I'm exploring the rcmail_session class to hunt down some intermittent issues with untimely session expiration, and to develop a better remember_me extension (or attempt to get it into core...).
I came across the following code
... /** * Setter for session lifetime */ public function set_lifetime($lifetime) { $this->lifetime = max(120, $lifetime);
// valid time range is now - 1/2 lifetime to now + 1/2 lifetime
$now = time();
$this->now = $now - ($now % ($this->lifetime / 2));
}
... /**
* Create session cookie from session data
*
* @param int Time slot to use
*/
function _mkcookie($timeslot)
{
$auth_string = "$this->key,$this->secret,$timeslot";
return "S" . (function_exists('sha1') ? sha1($auth_string) : md5($auth_string));
}
... /** * Check session authentication cookie * * @return boolean True if valid, False if not */ function check_auth() { ... if ($result && $this->_mkcookie($this->now) != $this->cookie) { ... }
It's quite deliberate, and it made me curious as to the reasoning behind the decision not to simply include a 'created_at' and 'expires_at' within the cookie, which would simplify the validation of the timespan. Is the reason for security, or perhaps a load-balancing?