Which AWS service should the company use to meet this requirement?

Explanations:

Amazon VPC is a networking service that allows users to create isolated networks within the AWS cloud. It does not manage logins or user authentication across AWS accounts.

Amazon GuardDuty is a threat detection service that continuously monitors for malicious activity and unauthorized behavior. It is not designed for managing user logins or identity access across accounts.

Amazon Cognito is a service for adding user sign-up, sign-in, and access control to web and mobile apps. While it handles user identities, it does not provide centralized access management across multiple AWS accounts in an organization.

AWS IAM Identity Center (formerly AWS Single Sign-On) is specifically designed for managing access to multiple AWS accounts within an organization. It allows for centralized user management and single sign-on capabilities across AWS accounts.