Answer: Amazon Cognito

The correct answer is B, Amazon Cognito. Amazon Cognito is a user identity and data synchronization service that provides secure user sign-up, sign-in, and access control. It supports not only traditional username and password authentication but also social logins through providers like Google, Facebook, and Amazon. This service is ideal for the scenario described in the question, where a company needs to allow users to log in to their web application using social identity providers.

Author: LeetQuiz Editorial Team