I have been looking into setting up a login for a web app that lets clients view data hosted in S3 and found that AWS Cognito has a hosted web UI [link] that handles most of
You can find more detail about how to make this work here -
https://aws.amazon.com/blogs/aws/launch-amazon-cognito-user-pools-general-availability-app-integration-and-federation/
http://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pools-ux.html
http://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pools-app-ui-customization.html