title: UserPool.getCurrentUser( ) returns null [backend]
body: <p>Am trying to set up a federated identity in order to get credentials for identity. But when i try to do the <strong>getCurrentUser()</strong> am getting response as null. And another thing about this is, am trying this on <strong>backend side</strong>. So will it work in the backend? And why am getting a null response when trying getCurrentUser ?? Any idea?</p>
  
  <pre><code>var data = {
      UserPoolId: userPoolId,
      ClientId: appClientId,
    };
  
  var userPool = new AmazonCognitoIdentity.CognitoUserPool(data);
  console.log(userPool);
  var cognitoUser = userPool.getCurrentUser();
  console.log(cognitoUser);
  </code></pre>
  
  <p>The log response of <strong>userPool</strong> is </p>
  
  <pre><code>CognitoUserPool {
      userPoolId: 'us-east-6_hxxxx2U',
      clientId: '`6heh4h8h848h4884h05',
      client:
       Client {
         endpoint: 'https://cognito-idp.us-east-1.amazonaws.com/',
         userAgent: 'aws-amplify/0.1.x js' },
      advancedSecurityDataCollectionFlag: true,
      storage:
       { [Function: MemoryStorage]
         setItem: [Function: setItem],
         getItem: [Function: getItem],
         removeItem: [Function: removeItem],
         clear: [Function: clear] } }
  </code></pre>
  
  <p>The log response of cognitoUser is <code>NULL</code></p>
  
  <p>So why is response null, while am giving right values as input?</p>