Session Destroy And Login Simulation

<?php

  /*
    Sessions
    - Unset And Destroy
    - Login And Logout Simulation
  */

  session_start();

  // $_SESSION['name'] = "Elzero";
  // session_unset();
  // session_destroy();

  if ($_SERVER["REQUEST_METHOD"] === "POST") {
    if ($_POST['user'] === "Osama") {
      $_SESSION['username'] = "Elzero";
      $_SESSION['id'] = 1005;
    }
  }

  echo '<pre>';
  print_r($_SESSION);
  echo '</pre>';

  if (isset($_SESSION['username'])) {
    echo "Welcome " . $_SESSION['username'];
  } else {

?>

<form action="" method="POST">
  <input type="text" name="user">
  <input type="submit" value="Login">
</form>

<?php } ?>

<a href="logout.php">Logout</a>

<?php

  session_start();
  session_unset();
  session_destroy();