How can existing systems be modified to incorporate a login feature in PHP?

To incorporate a login feature into an existing system in PHP, you can create a login form that collects user credentials, validate them against a database of users, and set a session variable upon successful login. This session variable can then be used to restrict access to certain parts of the system that require authentication. 

<?php
session_start();

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

    // Validate username and password against database
    if ($username == 'admin' && $password == 'password123') {
        $_SESSION['logged_in'] = true;
        header('Location: dashboard.php');
        exit();
    } else {
        $error = "Invalid username or password";
    }
}
?>

<!DOCTYPE html>
<html>
<head>
    <title>Login</title>
</head>
<body>
    <h2>Login</h2>
    <form method="post" action="">
        <input type="text" name="username" placeholder="Username" required><br><br>
        <input type="password" name="password" placeholder="Password" required><br><br>
        <button type="submit">Login</button>
    </form>
    <?php if(isset($error)) { echo $error; } ?>
</body>
</html>

Keywords

PHP login feature existing systems modification authentication

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