Amazon Cognito
Developer Guide

Configuring a User Pool Domain

After setting up an app client, you can configure the address of your sign-up and sign-in webpages. You can use an Amazon Cognito hosted domain and choose an available domain prefix, or you can use your own web address as a custom domain.

To add an app client and an Amazon Cognito hosted domain with the AWS Management Console, see Adding an App to Enable the Hosted Web UI.