Which AWS service or feature should the company use to meet these authentication requirements?

Explanations:

Amazon API Gateway is used to create, publish, maintain, and secure APIs at scale, but it does not provide temporary, limited-privilege credentials for AWS services.

IAM users are long-term credentials associated with individual users and do not provide temporary, limited-privilege access, which is required in this case.

AWS Security Token Service (AWS STS) provides temporary, limited-privilege credentials that allow applications to access AWS services securely and meet the authentication needs.

IAM instance profiles are used to provide temporary credentials to EC2 instances, but they are limited to EC2, not for a wide range of AWS APIs required by the application.