authenticate.php

<?php
session_start();
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "mywebsite";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $sql = "SELECT * FROM users WHERE username='$username'";
    $result = $conn->query($sql);
    if ($result->num_rows > 0) {
        $row = $result->fetch_assoc();
        if ($password === $row['password']) { // Plain text password comparison
            $_SESSION['username'] = $username;
            header("Location: welcome.php");
            exit();
        } else {
            echo "Invalid username or password";
        }
    } else {
        echo "Invalid username or password";
    }
}

$conn->close();
?>