Protection and safety.php

<?php
session_start(); // Start or resume a session

$host = 'your_host';
$dbname = 'your_dbname';
$user = 'your_username';
$pass = 'your_password';

try {
    $pdo = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    die("Could not connect to the database $dbname :" . $e->getMessage());
}

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST['username'];
    $password = $_POST['password'];

    $stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
    $stmt->execute(['username' => $username]);
    $user = $stmt->fetch();

    if ($user && password_verify($password, $user['password'])) {
        // Password is correct, so start a new session
        $_SESSION["loggedin"] = true;
        $_SESSION["id"] = $user['id'];
        $_SESSION["username"] = $username; 

        echo '<p style="color: green;">Login successful!</p>';
    } else {
        echo '<p style="color: red;">Invalid username or password!</p>';
    }
}
?>