What are best practices for handling user authentication and login systems in PHP using MySQL databases?

Issue: When handling user authentication and login systems in PHP using MySQL databases, it is important to securely store user passwords, validate user credentials, and protect against SQL injection attacks. 

// Example of handling user authentication and login in PHP using MySQL

// Connect to MySQL database
$mysqli = new mysqli("localhost", "username", "password", "database");

// Check if form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST["username"];
    $password = $_POST["password"];

    // Securely hash the password
    $hashed_password = password_hash($password, PASSWORD_DEFAULT);

    // Validate user credentials
    $query = "SELECT * FROM users WHERE username = '$username'";
    $result = $mysqli->query($query);

    if ($result->num_rows == 1) {
        $user = $result->fetch_assoc();
        if (password_verify($password, $user["password"])) {
            // User authenticated, redirect to dashboard
            header("Location: dashboard.php");
            exit();
        } else {
            // Invalid password
            echo "Invalid password";
        }
    } else {
        // User not found
        echo "User not found";
    }
}

Keywords

PHP MySQL user authentication login systems security

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