What best practices should be followed when handling user input in PHP, especially in the context of login forms?

When handling user input in PHP, especially in the context of login forms, it is crucial to sanitize and validate the input to prevent security vulnerabilities such as SQL injection and cross-site scripting attacks. One best practice is to use prepared statements with parameterized queries to prevent SQL injection. Additionally, input validation should be done to ensure that the data provided by the user meets the expected format and length. 

// Sanitize and validate user input for a login form
$username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);
$password = filter_var($_POST['password'], FILTER_SANITIZE_STRING);

// Validate input
if (empty($username) || empty($password)) {
    // Handle error, e.g. display a message to the user
} else {
    // Use prepared statements to prevent SQL injection
    $stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND password = :password");
    $stmt->execute(['username' => $username, 'password' => $password]);

    // Check if the user exists and the password is correct
    if ($stmt->rowCount() > 0) {
        // User authenticated, proceed with login
    } else {
        // Handle error, e.g. display a message to the user
    }
}

Keywords

validation sanitization prepared statements password hashing CSRF protection

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