An authoritative source in cybersecurity and Identity and Access Management (IAM) refers to the single, most trusted system or repository that holds the definitive, accurate, and complete version of critical data. It serves as the "single source of truth" for specific information sets, such as digital identities, user attributes, roles, and access entitlements. Different types of data may have distinct authoritative sources—for example, an HR system might be authoritative for employee status and personal details, while a directory service could be authoritative for group memberships and system permissions.

Reliance on clearly defined authoritative sources is fundamental to maintaining a strong security posture. It minimizes data discrepancies, reduces the risk of privilege creep, prevents unauthorized access from outdated or conflicting information, and streamlines compliance efforts. Without properly designated and governed authoritative sources, organizations face significant challenges in ensuring identity data accuracy and consistency, leading to operational inefficiencies and heightened security vulnerabilities.