Security with ini files and php header - php

Question

I'm currently in the process of developing a simple CMS for ONE user (this is unlikely to ever change). Therefore I'm storing login details in a .ini file (when live, will be stored outside root). Then using sessions to detect if the correct user has logged in, and if not, redirect them back to the login page using Header('Location: login.php') I'm curious as to how secure this actually is? Below is a draft of what I've got so far
Login Page:
<?php
session_start();
if ($_GET) {
header("Location: login.php");
die();
}
if (isset($_SESSION['user'])) {
header('Location: admin/index.php');
}
$config = parse_ini_file("login.ini", true);
$user = htmlentities($_POST['user']);
$password = htmlentities($_POST['pass']);
if ($user == $config['login']['user'] && $password == $config['login']['password']) {
$_SESSION['user'] = $_POST['user'];
header('Location: admin/index.php');
}
?>
<form action="login.php" method="POST">
<h2>Username:</h2>
<input type="text" name="user" />
<h2>Password:</h2>
<input type="password" name="pass" />
<input type="submit" Value="Login" />
</form>
Then there would be a check on every page in the admin area for the session, if not redirect to the login using the header location, like so:
Admin Welcome Page
<?php
session_start();
if (!isset($_SESSION['user'])) {
header('Location: ../login.php');
die();
}
And a logout page, would destroy the session.
I understand this is fairly simple and doesn't use a database. But are there any major secruity flaws to this design, using header location a lot, and storing sensitive date in the .ini file. Or for a simple application, is this well suited / not outdated?