title: firebase ".read": "auth != null && auth.uid == $uid" not working as expected
body: <p>I started today with Firebase and try to create a sample iOS app.
  At the moment I'm stuck with securing my data.</p>
  
  <p>Lets say I have this demo data.</p>
  
  <pre><code>{
   "Demodata" : {
     "demodata-1" : {
        "id" : 1,
        "uid" : 1234
     }
   } 
  }
  </code></pre>
  
  <p>and this rule file</p>
  
  <pre><code> {
    "rules": {
      "Demodata" : {
        "$uid" : {
          ".read" : "auth.uid == $uid" 
        }
      }
    }
  }
  </code></pre>
  
  <p>and a logged in user with the uid : 1234</p>
  
  <p>I log in with this code.</p>
  
  <pre><code> ref.authUser(email, password: password,
          withCompletionBlock: { error, authData in 
             completion(result: error)
   })
  </code></pre>
  
  <p>Then I try to get the data with this code.</p>
  
  <pre><code>  demoDataRef.queryOrderedByChild("id").queryEqualToValue(queryValue).observeSingleEventOfType(.Value, withBlock: { snapshot in
          // do some stuff once
          print(snapshot)
      })
  </code></pre>
  
  <p>But I never get the data back from Firebase. When I remove the rule and add a ".read" : true to the parent everything works.</p>
  
  <p>I'm sure I miss something but at the moment I'm a little bit lost. Maybe some one can point me in to the right direction.</p>