How to use $_SESSION in right way? - php

Question

At the moment I am writing a little media library in PHP and i want to set sessions, so the user stays logged in and get's echoed his name at the front page.
[index.php]
if(isset($_SESSION['loggedin']))
{
//ECHO $USERNAME
}else{
echo '<p>To start, please login or register.</p>';
}
?>
I want, if theres an session id set, that PHP echoes out the $username.
[signup.php]
<?php
session_start();
$conn = mysqli_connect("$host", "$user", "$pass", "$db");
$uid = ($_POST['uid']);
$pw = ($_POST['pw1']);
$pw2 = ($_POST['pw2']);
if ($pw == $pw2) {
$sql = "INSERT INTO user (uid, pw) VALUES ('$uid', '$pw')";
$result = mysqli_query($conn, $sql);
echo "Registration succeeded.";
}else{
echo "Please check your information.";
}
header ("Refresh: 3; ../index.php");
So, after PHP successfully compares my $pw1 and $pw2 i want to start a session, then it should put the $username in the $_SESSION array.
Of course next to the secure session id.
I repeat, after this i want to echo the $username out at front page.
What is the best way to do it?
Thanks.

Answer 1

$sql="SELECT username FROM users WHERE userid=$uid";
$result=mysqli_query($conn,$sql);
$row=mysqli_fetch_assoc($result);
$_SESSION['username']=$row['username'];
You can do something like this.

Answer 2

Usage of $_SESSION super global array (compact version)
session_start(); //To init
$_SESSION['username'] = 'Bob'; // Store value
echo $_SESSION['username']; // Treat like normal array
Detailed example
To use a session, you have to init it first.
session_start();
After that you access the session vars via the super global
$_SESSION
A good way is always to store a value in your variables you want to use:
// init session
session_start();
// check if session var is set, if not init the field with value in the super global array
if(!isset($_SESSION['auth'])) $_SESSION['auth'] = false;
if(!$_SESSION['auth']) {
//do auth here like eg.
header('Location: signup.php'); // if auth is okay -> $_SESSION['auth] = true + redirect to this (main) script
die(); // This is really necessary because a header redirect can be ignored.
}
// if auth okay, do fancy stuff here
For security read the following
Remember to escape your user input, always!
How can I prevent SQL injection in PHP?
The session_id is stored in cookies normally.
Or - the old way via URL parameter.
You do not have to secure the session_id.
Read also advices about XSS/CSRF.
Plus tokens are also good.
May be this is what you mean with secure session_id.
Stackoverflow: preventing csrf in php
OWASP: https://www.owasp.org/index.php/PHP_CSRF_Guard
OWASP: https://www.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet