<?php
session_start();

$cachedFile = 'randomNumbers.txt';
CONST USER = 'bob'; CONST PASS = 'test';

if ($_POST['name'] == USER && $_POST['pass'] == PASS) {
    //log them in
    $_SESSION['loggedIn'] = true;
}

$useCache = ($_SESSION['loggedIn'] !== true);

//let's see if the cache is stale
if (!$useCache || (file_exists($cachedFile) && ((time() - filemtime($cachedFile)) > 3))) {

    //yep, it's stale - regenerate
    ob_start();

    $randomNumbers = array();
    foreach (range(0,9) as $index) {
        $randomNumbers[$index] = rand(1, 100);
    }

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

    echo '<form method="POST">Name: <input name="name"> Pass: <input name="pass"> <input type="submit" value="Login"></form>';

    //write output to temp file
    file_put_contents($cachedFile, ob_get_contents());

    ob_end_flush();
} else {
    readfile($cachedFile);
}