title: Facebook Messenger Platform: how to get user specific information?
body: <p>I'm trying the recent released Facebook Messenger Platform and so far so good. Everything worked well and I was able to create a echo bot.</p>
  
  <p>But I'm wondering how I could identify this user that started chatting in my page. For example, when a user started chatting I get a PID user (page specific user id).</p>
  
  <p>Making the follow request to Facebook Graph API:</p>
  
  <pre><code>GET https://graph.facebook.com/v2.6/{PAGE_SPECIFIC_USER_ID}
  </code></pre>
  
  <p>I discovered that I can just ask for the following fields: first_name,last_name and profile_pic.</p>
  
  <p>So my question is, how could I discover if this user is a current customer of my business page? Is there another way of querying more information (like e-mail and real facebook user id)?</p>