User Pool Authentication Flow – Amazon Cognito

A user migration Lambda trigger allows easy migration of users from a legacy user management system into your user pool. To avoid making your users reset their passwords during user migration, choose the USER_PASSWORD_AUTH authentication flow. This flow sends your users’ passwords to the service over an encrypted SSL connection during …

https://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-user-pools-authentication-flow.html