Sessions & Cookies

PHP

⏱ 18 min read📖 BeginnerNot completed

HTTP is stateless — each request is independent. Sessions and cookies allow you to persist data across multiple page requests, which is essential for user authentication.

Sessions

Sessions store data on the server. A session ID is stored in a cookie on the client.

PHP

<?php
// MUST be called before any output!
session_start();

// Set session data
$_SESSION["username"] = "john";
$_SESSION["user_id"]  = 42;
$_SESSION["logged_in"] = true;

echo "Session started!";
?>

Reading Session Data

PHP

<?php
session_start();

// Check if logged in
if (isset($_SESSION["logged_in"]) && $_SESSION["logged_in"] === true) {
    $username = $_SESSION["username"];
    echo "Welcome, $username!";
} else {
    echo "Please log in.";
    header("Location: login.php");
    exit();
}
?>

Destroying a Session (Logout)

PHP

<?php
session_start();

// Remove specific session variable
unset($_SESSION["username"]);

// Remove ALL session data
session_unset();

// Destroy the session completely (logout)
session_destroy();

header("Location: login.php");
exit();
?>

Cookies

Cookies store data in the user's browser. They persist even after the browser is closed.

PHP

<?php
// Set a cookie (expires in 30 days)
setcookie(
    "username",          // name
    "john",              // value
    time() + (30 * 24 * 60 * 60),  // expiry
    "/",                 // path
    "",                  // domain
    true,                // secure (HTTPS only)
    true                 // httponly (no JavaScript access)
);

// Read cookie
if (isset($_COOKIE["username"])) {
    echo "Welcome back, " . $_COOKIE["username"];
}

// Delete cookie (set expiry in past)
setcookie("username", "", time() - 3600, "/");
?>

Sessions vs Cookies

	Sessions	Cookies
Storage	Server	Browser
Security	More secure	Less secure
Persistence	Until browser closes	Until expiry date
Size limit	No limit	4KB max
Use for	Login state, cart	Remember me, preferences

💡

Laravel handles sessions automatically! Use session('key', 'value') to set and session('key') to get. Laravel also has flash messages: session()->flash('success', 'Saved!')

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