Answer: Amazon Cognito

## Explanation Amazon Cognito is the correct service for this scenario because: - **Amazon Cognito** is specifically designed for mobile and web applications that need user sign-up, sign-in, and access control - It can scale to handle thousands of users accessing a mobile app - Provides user directories and authentication flows for mobile apps - Supports social identity providers (Google, Facebook, etc.) and enterprise identity providers - Manages user profiles and authentication state **Why the other options are incorrect:** - **AWS Directory Service**: Primarily for enterprise directory services like Active Directory, not optimized for mobile app user authentication - **AWS IAM Identity Center**: Used for centralized access management to multiple AWS accounts and business applications, not specifically for mobile app user directories - **AWS Identity and Access Management (IAM)**: Used for managing AWS resource access for AWS users, not for managing end-user authentication for mobile applications For mobile applications with thousands of users requiring sign-in capabilities, Amazon Cognito is the recommended AWS service.

Author: Ritesh Yadav