Source of: /ADI/auth-db-sessions/login_action.php

<?php
include_once 'inc/db.php';

session_start();


if( !isset($_POST['uid']) or !isset($_POST['pwd']) )
  header("Location: login_failed.html");


$uid = $_POST['uid'];
$pwd = $_POST['pwd'];

$db = dbconnect($hostname,$db_name,$db_user,$db_passwd);
$query = "SELECT * FROM users
         WHERE userid = '$uid'
           AND password = '$pwd'";
$result = @ mysqli_query($db,$query);
if (!$result)
  error('A database error occurred while checking your login details.');

if (mysqli_num_rows($result) == 0) {
  unset($_SESSION['uid']);
  header("Location: login_failed.html");
}
else {
   $tupple = mysqli_fetch_assoc($result);
   $_SESSION['username'] = $tupple['fullname'];
   $_SESSION['email'] = $tupple['email'];
   $_SESSION['notes'] = $tupple['notes'];
   $_SESSION['uid'] = $tupple['userid'];
}

mysqli_close($db);

header("Location: index.php");
?>