Which AWS service will meet these requirements?

Explanations:

AWS Directory Service is primarily used for setting up and managing Microsoft Active Directory in the cloud. It does not provide a direct way for users to log in to web applications using social identity providers.

Amazon Cognito is specifically designed for user authentication and allows users to sign in through social identity providers such as Google, Facebook, and Amazon. It manages user identities and provides secure access to applications.

AWS Identity and Access Management (IAM) is used for managing access to AWS resources and does not offer functionality for user authentication through social identity providers for web applications. It is primarily focused on AWS service permissions.

AWS Single Sign-On (SSO) is intended for enterprise-level access management and does not support direct login through social identity providers for web applications. It is more suited for managing access to multiple AWS accounts and business applications.