Use existing Cognito User Pools & Identity Pools for your Amplify project

With today’s Amplify CLI release, you gain the ability to import existing Amazon Cognito resources into your Amplify project. Just run the “amplify import auth” command and Amplify CLI will automatically configure all your Amplify-provisioned resources (GraphQL APIs, S3 buckets and more) to be authenticated with your designated existing Cognito User Pool or Identity Pool.  

Source:: Amazon AWS