PHP Login Index

<?php

    session_start();

    if(!isset($_SESSION["id"]) || !isset($_SESSION["username"])){

    }else{
        header("Location: painel.php");
    }


    if(isset($_POST['login'])){
        require("/data/config.inc.php");

        $username = strip_tags($_POST['username']);
        $password = strip_tags($_POST['password']);

        $username = stripslashes($username);
        $password = stripslashes($password);

        $username = mysqli_real_escape_string($db, $username);
        $password = mysqli_real_escape_string($db, $password);

        $password = md5($password);

        $sql = "SELECT * FROM usuarios WHERE username = '$username' LIMIT 1";
        $query = mysqli_query($db, $sql);
        $row = mysqli_fetch_array($query);
        $id = $row['id'];
        $db_password = $row['password'];

        if($password = $db_password){
            $_SESSION['username'] = $username;
            $_SESSION['id'] = $id;
            header("Location: painel.php");
        }else{
            echo 'Usuario ou senha incorretos';
        }

    }
?>

<html>
    <head>
    <title> Login Pluz VS</title>
    <meta charset="UTF-8">
    </head>

    <body>
        <form action="" method="post" enctype="multipart/form-data">
            <input placeholder="Usuario" name="username" type="text">
            <input placeholder="Senha" name="password" type="password">
            <input value="Login" name="login" type="submit">

        </form>
    </body>


</html>