AWS Certified Cloud Practitioner

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.