A company uses an organization in AWS Organizations to manage its 250 member accounts.

AWS CloudTrail is theauthoritative source for identity-related activityacross an AWS Organization. According to the AWS Certified Security – Specialty Official Study Guide, CloudTrail recordsall AWS API calls and authentication events, including federated sign-ins that occur through AWS IAM Identity Center with an external SAML identity provider.

When IAM Identity Center is used,successful federated login events are logged in CloudTrailas ConsoleLogin and AssumeRoleWithSAML events. These events are recorded in theorganization’s management accountwhen CloudTrail is configured as an organization trail. This allows security teams to centrally search and correlate authentication activity across all member accounts.

Option A is incorrect because CloudWatch Logs do not natively aggregate authentication events across an organization unless custom pipelines are built. Option B is not scalable and does not provide historical, organization-wide visibility. Option C is invalid because AWS does not ingest external IdP logs into EventBridge automatically, and IdP logs do not reflect AWS-side role assumptions.

AWS documentation explicitly states thatCloudTrail organization trails provide centralized visibility into user authentication and access activity across all accounts, making this the fastest and most reliable way to identify when a user logged in during a specific time window.

AWS Certified Security – Specialty Official Study Guide

AWS CloudTrail User Guide

AWS IAM Identity Center Documentation

AWS Organizations Best Practices