Which AWS service or resource should the developer use to meet these requirements?

Explanations:

IAM roles are used for managing permissions for AWS resources, not for user authentication or registration via social media accounts.

Amazon Cognito identity pools provide temporary AWS credentials for federated identities, but they don’t directly manage user registration or authentication through social media accounts.

Amazon Cognito user pools are specifically designed for user authentication, including supporting social media logins like Facebook, Google, and others, making it the right choice for user registration via social media accounts.

AWS Directory Service is used to set up and manage Microsoft Active Directory on AWS, and is not suitable for handling user registration or authentication via social media accounts.