Cognito

Cognito is Amazon’s proprietary framework for authentication and authorization. Cognito allows for user login via an app-specific user credential or existing Amazon or third-party accounts (Such as Google or Facebook), with app users collected in repositories called User Pools. Authenticated users then use the credentialing provided by Cognito to access AWS-serviced app features or content (depending on authorization level).

The following diagram from AWS’s Cognito docs illustrates the request sequence for users through an integrated app:

Cognito Auth/Auth pathway

Cognito has many defaul settings and UI elements available, and allows for configuration of username and password requirements, account confirmation via email address or multi-factor authentication.
On Android, Cognito requires the integrating app be bult around Android API 16 or later and use Amplify libraries. (Commands for configuring an existing project for Cognito features are available here).