title: Paypal return a post variable (or equivalent?)
body: <p>I'm building a simple PHP web app that uses Paypal to add credit to an account. (I've just got the basic "Website Payments Standard" account)</p>
  
  <p>Have spent the last hour looking on Paypal's site and Google, but can't find a simple way to return a success variable.</p>
  
  <p><strong>Ideal Scenario</strong></p>
  
  <ol>
  <li>Buyer clicks 'add credit' on my site and is redirected to Paypal (this part is easy)</li>
  <li>Buyer fills in credit card details and payment approved.</li>
  <li>A variable is posted back to my site (or the equivalent of this) to confirm payment success</li>
  <li>My website converts the variable into an account credit.</li>
  </ol>
  
  <p>It doesn't need to be the most hack-proof thing in the world, but obviously can't just put the success status in the url and use GET!</p>
  
  <p>Thanks heaps!</p>