Which AWS service or resource will meet this requirement?

Explanations:

AWS Organizations allows you to manage multiple AWS accounts, but it does not provide a way to authenticate users across these accounts with a single set of credentials.

An IAM user is specific to a single AWS account and cannot be used to authenticate across multiple accounts with a single set of credentials.

AWS IAM Identity Center (AWS Single Sign-On) enables users to access multiple AWS accounts and applications with a single set of credentials, streamlining authentication and authorization.

AWS Control Tower helps set up and govern multi-account AWS environments but does not provide single sign-on capabilities or manage user authentication across accounts.