title: How to get the preapprovalKey using PayPal Adaptive Payments API only if user completes the preapproval process?
body: <p>I'm using the PayPal Adaptive Payments. I have succesfully redirected the user to the PayPal preapproval process for some periodic/automatic payments our product needs. However, I have the following issue.</p>
  
  <p>When the user is redirected to the logging screen on PayPal for the preapproval process, even if the user has not signed in yet, PayPal already gives me a preapproval JSON with the key: </p>
  
  <pre><code>    { responseEnvelope: 
      { timestamp: '2013-11-28T18:38:58.726-08:00',
      ack: 'Success',
      correlationId: 'XXXXXXX',
      build: 'XXXXXXX' },
      preapprovalKey: 'PA-XXXXXXX',
      httpStatusCode: 200,
      preapprovalUrl: 'https://www.sandbox.paypal.com/webscr?cmd=_ap-preapproval&amp;preapprovalkey=PA-XXXXXXX' }
  </code></pre>
  
  <p>However, the big issue here is that I should not save the preapprovalKey yet on my DB, because the user could abort the preapproval process since he/she has not signed in yet. I should save it, only if the user complete the process.</p>
  
  <p><strong>I would like to know if there is a method to get the preapproval response <em>only if the users finishes the preapproval process</em>.</strong> </p>
  
  <p>Thanks for your time.</p>