title: AWSCognito Missing region in config error
body: <p>I'm using the <code>aws-sdk javascript</code> in my back-end and I can use <code>AWS</code> fine but when I try to use the <code>getOpenIdTokenForDeveloperIdentity</code> method I get a <code>"Missing region in config error"</code> as a response.</p>
  
  <pre><code>var config = new AWS.Config({
    accessKeyId: "MYACCESSKEY", secretAccessKey: "MYSECRETYKEY", region: 'us-east-1'
  });
  
  var params = {
    IdentityPoolId: 'MYIDENTITYPOOLID', /*   required */
    Logins: { /* required */
      "login.my.myapp": 'string',
      /* anotherKey: ... */
    },
    IdentityId: null,
    TokenDuration: 0
  };
  
  cognitoidentity.getOpenIdTokenForDeveloperIdentity(params,function(err, data) {
    if (err) console.log(err, err.stack); // an error occurred
    else console.log(data);               // successful response
  });
  </code></pre>
  
  <p>In the docs it said that:</p>
  
  <blockquote>
    <p>By default, credentials and region settings are left unconfigured. This should be configured by the application before using any AWS service APIs.</p>
  </blockquote>
  
  <p>So I set my region but why am I still getting an error?</p>