An authentication service is a fundamental cybersecurity component designed to verify the digital identity of users, systems, applications, or devices attempting to access protected resources. It forms the cornerstone of Identity & Access Management (IAM) strategies by evaluating presented credentials—such as passwords, biometrics, security tokens, or digital certificates—against an authoritative database of trusted identities to establish whether access should be permitted.

When credentials successfully match verified identity data, the authentication service confirms the entity's authenticity, enabling subsequent access control decisions. This process is essential for maintaining data integrity, confidentiality, and organizational security. Modern authentication services frequently implement multi-factor authentication (MFA) to strengthen protection against unauthorized access and evolving cyber threats.