For a secure and constantly updated login solution, Amplify uses services provided by Auth0 https://auth0.com/docs.
Implementation
During signup, the user is presented with a sign-up page which is hosted by Auth0 and styled to match the look of Amplify. The page allows the user to input an email and a password for login to Amplify. During the sign-up process, a confirmation email will be sent to the user to confirm the sign-up. When this has been confirmed, the user will then be able to log in.
Authentication flows are hosted by Auth0 and all authentication is handled by Auth0, before being redirected to the Amplify service hosted on AWS.
The implementation is based on the https://auth0.com/docs/authenticate/login/auth0-universal-login/new-experience#introduction service which provides the frontend and backend services for the signup and login experience required for Amplify.
All data required for this process is stored in Auth0.
Enterprise authentication
The implementation allows for Single Sign-On (SSO) and Silent Authentication which supports any social or enterprise connection set up to integrate with Auth0 and Amplify. Integration to a customer SSO interface is done on a case-by-case basis.
At Enterprise level, users of Amplify are separated into separate tenants, which allows complete segregation of user data.