<?php
session_start();
$userArray = array(
	"username1" => "password1",
	"username2" => "password2",
	"username3" => "password3"
);

if (isset($_SESSION['user']))
{
	$logout=true;
	foreach($userArray as $username)
	{
		if ($username == $_SESSION['user'])
			$logout=false;
	}
	if (isset($_GET['logout'])||$logout=true;)
	{
		session_destroy();
		header("Location: ./");
	}

	//logged in stuff goes here
}
else
{
	if (isset($_POST['username']))
	{
		$username = $_POST['username'];
		$password = $_POST['password'];

		if ($userArray[$username] == $password)
		{
			$_SESSION['user'] = $username;
			header("Location: ./");
		}
		else
		{
			//fail
		}
	}

	?>
	<form method="post">
	Username: <input name="username" /><br/>
	Password: <input name="password" /><br/>
	<input type="submit" value="Login" />
	</form>
	<?php
}
?>