In the context of the provided code, what improvements can be made to ensure the functionality works as intended without compromising security?

The issue in the provided code is that it directly concatenates user input ($_POST['username']) into the SQL query, making it vulnerable to SQL injection attacks. To ensure functionality without compromising security, we should use prepared statements with parameterized queries to sanitize user input and prevent SQL injection. 

// Issue: SQL injection vulnerability
$username = $_POST['username'];
$password = $_POST['password'];

// Fix: Use prepared statements with parameterized queries
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND password = :password");
$stmt->execute(['username' => $username, 'password' => $password]);

// Check if user exists
if ($stmt->rowCount() > 0) {
    // User authenticated
} else {
    // User not found
}

Keywords

SQL injection prepared statements password hashing cross-site scripting secure file uploads

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