Session

Session support in PHP consists of a way to preserve certain data across subsequent accesses to the web server.

By default, each query to a webserver is independent from the others. With session, it is possible to keep some data on the server, and retrieve them at each access.

It relies on the session_* functions, and the $_SESSION superglobal variable.

<?php

    if (isset($_SESSION['x'])) {
        print 'x was already set with the value ' . $_SESSION['x'];
    }

    $_SESSION['x'] = rand(0, 10);
    print 'Giving the value ' . $_SESSION['x'] . 'to x, in the session';

?>

Documentation

See also Session in PHP: Creating, Destroying, and Working With Session in PHP, Sessions security and Fixing PHP Session Issues: Troubleshooting and Solutions.

Related : Superglobal Variables, Object Persistence, Persistence, Session Fixation, Session Hijacking, Horizontal Scaling, Race Condition, Single Sign On (SSO), State, JSON Web Token (JWT), Load Balancer, SessionHandlerInterface, SessionIdInterface, SessionUpdateTimestampHandlerInterface