title: aws cognito verify sub of a newly signed up user
body: <p>For a newly signed up user using Cognito Javascript SDK, it looks like we can get the 'sub' value, as per <a href="https://github.com/aws/amazon-cognito-identity-js/issues/335#issuecomment-307523556" rel="nofollow noreferrer">https://github.com/aws/amazon-cognito-identity-js/issues/335#issuecomment-307523556</a></p>
  
  <p>If I pass this 'sub' value to my backend to initialize this user in the database, what's the best way to verify if this is a newly signed up valid user's sub?</p>