title: AWS Cognito/Amplify - have new user sign ups be automatically add to a user group
body: <p>I am using AWS Amplify library to sign up and perform Auth for an AppSync project.   This uses Cognito.  However, when a new user signs up via Amplify/Cognito, the new user isn't assigned to any specific group in the cognito pool.  I am using the Amplify higher order component for login/signup.</p>
  
  <pre><code>import { withAuthenticator } from 'aws-amplify-react';
  </code></pre>
  
  <p>which I wrap over a component</p>
  
  <pre><code>class Authenticator extends React.Component {
     //... basically empty component, only exists so I can wrap it w/ the HOC
  }
  export default withAuthenticator(Authenticator)
  </code></pre>
  
  <p>Amplify is set up in index.js</p>
  
  <pre><code>import config from './aws-exports';
  import Amplify from 'aws-amplify';
  Amplify.configure(config);
  </code></pre>
  
  <p>aws-exports.js was autogenerated by AWS Mobile Hub CLI.  Looks like...</p>
  
  <pre><code>const awsmobile = {
      'aws_app_analytics': 'enable',
      'aws_cognito_identity_pool_id': 'us-west-2:XXX',
      'aws_cognito_region': 'us-west-2',
      'aws_content_delivery': 'enable',
      'aws_content_delivery_bucket': 'flashcards-hosting-mobilehub-XXX',
      'aws_content_delivery_bucket_region': 'us-west-2',
      'aws_content_delivery_cloudfront': 'enable',
      'aws_content_delivery_cloudfront_domain': 'XXX.cloudfront.net',
      'aws_mandatory_sign_in': 'enable',
      'aws_mobile_analytics_app_id': 'XXX',
      'aws_mobile_analytics_app_region': 'us-east-1',
      'aws_project_id': 'XXX',
      'aws_project_name': 'flash-cards',
      'aws_project_region': 'us-west-2',
      'aws_resource_name_prefix': 'flashcards-mobilehub-XXX',
      'aws_sign_in_enabled': 'enable',
      'aws_user_pools': 'enable',
      'aws_user_pools_id': 'us-west-2_XXX',
      'aws_user_pools_mfa_type': 'OFF',
      'aws_user_pools_web_client_id': 'XXX',
  }
  export default awsmobile;
  </code></pre>