WP-Subscription Example

subs.php

<?php
	header('HTTP/1.1 200 OK');
	/**
	 * @package WordPress
	 * @var bool
	 */
	define('WP_USE_THEMES', false);
	/** Loads the WordPress Environment and Template */
	require('./wp-blog-header.php');
	$current_user = wp_get_current_user();
	if($_REQUEST['paid'] == "yes")
	{
		//successful payment
		update_usermeta($current_user->ID, 'subscription', "true");
		update_usermeta($current_user->ID, 'trialDone', 0); //to remove from user_meta
		update_usermeta($current_user->ID, 'trialDays', 0); //to remove from user_meta
	}
	else {
		$subscription = get_user_meta($current_user->ID, 'subscription', true);
		$trialDays = get_user_meta($current_user->ID, 'trialDays', true);
		$trialDone = get_user_meta($current_user->ID, 'trialDone', true);
		if ($current_user->ID  == 0) {
		//not logged in
			}
		if($subscription != "true")
		{
			if($trialDone == "true")
				{
					//trial has ended in a previous session
				}
				else {
					if(empty($trialDays))
					{
						//give 5 days for a trial
					}
					else if (intval($trialDays) < 1)
					{
						//trial has ended in a previous session
					}
					else if((intval(time()) - intval($_COOKIE['seshCurrent'])) > 80000) //24 hours
					{
						$newTrialDays = intval($trialDays) -1;
						if($newTrialDays  == 0)
						{
							//trial has now ended
						}
						else {
							//$trialDays remaining
							setcookie("seshCurrent",time(), time()+3600*24*7);
					}
				}
			}
		}
	}
?>

Related Blog Post: http://blog.yasyf.com/2012/07/31/using-wordpress-as-a-pay-for-access-system/