title: Check to see if Facebook post exists
body: <p>I have an app (or link really) that allows my customer to share a certain product to their wall/timeline through this protocol:</p>
  
  <p><a href="http://www.facebook.com/dialog/feed?app_id=APP_ID&amp;link=" rel="nofollow">http://www.facebook.com/dialog/feed?app_id=APP_ID&amp;link=</a>....</p>
  
  <p>Upon successful share, the customer gets a coupon code, once he/she is directed back to my site.</p>
  
  <p>I'd like to be able to verify the existence of the share post to determine if the rebate code is valid or not. I have the post id, looking like this:</p>
  
  <p>704745000_513399762010000 (random example)</p>
  
  <p>I kind of figured out that I need permission to query for a specific post using graph-api in a users timeline, but how can I get the permission? Any pointers and examples (in php) are appreciated, thanks.</p>