validate.php

<?php
session_start();

$username = $_POST['username'];
$password = $_POST['password'];



$user = "wilson";
$pass = "españita";

if(isset($_SESSION['username'])){
    header("Location: panel.php");
}else {
    if($username == "" || $password == ""){
        $_SESSION["errorVacio"] = "<b>Error:</b>  Tienes que rellenar el formulario";
        header("Location: index.php");
    }
    if(($username != $user && $username!="") || ($password != $pass && $password!="")){
        $_SESSION["errorSession"] = "<b>Error:</b> El Username o el Password son incorrecto, por favor vuelve a intentarlo";
        header("Location: index.php");
    }
    
    if ($username == $user && $password == $pass) {
        $_SESSION['username']=$user;
        $_SESSION['password']=$pass;
        header("Location: panel.php");
        
    }
}