What AWS service provides temporary credentials for unauthenticated and authenticated users?

Amazon Cognito Identity Pool is the correct choice because it is specifically designed to provide temporary AWS credentials to both authenticated and unauthenticated users. This service allows developers to create a seamless user experience by managing user identity and access while facilitating access to other AWS services.

With an Identity Pool, you can grant unauthenticated users limited access to AWS resources, such as allowing guests to use your application without requiring them to sign in. For authenticated users, Cognito can integrate with various identity providers (like social logins or enterprise SSO), providing a smooth transition to accessing AWS services with the appropriate permissions.

This service is particularly useful in mobile and web applications where the user base can vary widely in terms of authentication status. Additionally, the temporary credentials generated through Cognito are automatically refreshed, avoiding the need to manage long-lived access keys securely.

In contrast, IAM Roles are used to define permissions for AWS resources but do not inherently provide the management of users or their authentication status. Amazon QuickSight is a business analytics service, and S3 Access Control Lists relate specifically to granting permissions on Amazon S3 buckets and objects rather than user authentication and temporary credential management.