Very quick and dirty login, just add this entire script above the stuff in your index.php file.

quick_and_dirty_login.php

<?php
  // SET YOUR USER/PASS STUFF HERE...
  $auth = array(
    'user1' => 'pass123',
    'user2' => 'pass123',
    'user3' => 'pass123',
    'user4' => 'pass123',
    'user5' => 'pass123',
  );
  
  
  /////////////////////////////////////////////////
  // DON'T WORRY ABOUT THIS CRAP
  /////////////////////////////////////////////////
  session_cache_limiter('private');
  $cache_limiter = session_cache_limiter();
  session_cache_expire(60 * 24);
  $cache_expire = session_cache_expire();
  session_start();
  header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
  header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
  
  function showLogin(){
    echo 'login';
    $form = '<form method="post" action="" name="login">';
    $form .= 'User: <input name="user" type="text" />';
    $form .= '<br>';
    $form .= 'Pass: <input name="pass" type="text" />';
    $form .= '<input name="submit" type="submit" value="Login" />';
    $form .= '</form>';
    echo $form;
    die();
  }
  
  $showLogin = true;
  $user = (isset($_POST['user'])) ?  @$_POST['user'] : '';
  $pass = (isset($_POST['pass'])) ?  @$_POST['pass'] : '';
  if( isset($_SESSION['authenticated']) && $_SESSION['authenticated'] == true ){
    $showLogin = false;
  } else if (isset($_POST['user']) && isset($_POST['pass'])){
    // Check Login
    if(isset($auth[$user]) && $auth[$user] === $pass){
      $_SESSION['authenticated'] = true;
      $showLogin = false;
    }
  }
  
  if($showLogin == true){  showLogin(); }
?>