title: Aws Cognito: How to assign user to a user group when user signs up
body: <p>I have below user groups in aws cognito.
  Admin
  Member
  Paid member </p>
  
  <p>I want to assign all user to Member user group as default when they sign up on my application so I can assign different IAM role on that user group.</p>
  
  <p>How do I assign user to a user group programmatically?</p>