Which AWS service supports user sign-up functionality and authentication to mobile and web applications?

Amazon Cognito provides authentication, authorization, and user management for web and mobile applications. It enables user sign-up and sign-in with various identity providers, and manages user directories, making it ideal for securing application access.

AWS Config assesses, audits, and evaluates the configurations of AWS resources, unrelated to user authentication.

Amazon GuardDuty is a threat detection service, not an identity management or authentication service.

AWS Systems Manager helps users gain operational insights and take action on AWS resources, not directly for user sign-up and authentication for applications.