php sessions to authenticate user on login form

Question

I have the following code designed to begin a session and store username/password data, and if nothing is submitted, or no session data stored, redirect to a fail page.

Answer 1

Don't use else section in second if statement.

session_start();

if(isset($_POST['username']) || isset($_POST['password'])) {

    $username = $_POST['username'];

    $password = $_POST['password'];

    $_SESSION['username'] = $username;

    $_SESSION['password'] = $password;

}

if(isset($_SESSION['username']) || isset($_SESSION['password'])){

    $navbar = "1";

    $logindisplay = "0";

    $username = $_SESSION['username'];

    $password = $_SESSION['password'];

}

$authed = auth($username, $password);

if( $authed == "0" ){

    header('Location:http://website.com/fail.php');

}