Which AWS service issues temporary, federated security credentials to allow access to AWS resources?

AWS Security Token Service (AWS STS) is the correct answer because it enables you to request temporary, limited-privilege credentials for AWS Identity and Access Management (IAM) users or for users authenticated through a federation. This is crucial for granting secure, time-bound access to AWS resources without managing long-term credentials. Amazon GuardDuty is a threat detection service, not for issuing credentials. AWS Secrets Manager securely stores and manages secrets like database credentials, API keys, and other sensitive data, but it doesn't issue temporary security credentials. AWS Certificate Manager provisions, manages, and deploys SSL/TLS certificates, which are for encryption and identity, not for federated access credentials.