authentication

Authentication is the process of verifying the identity claimed by a user, device, or other entity before granting access to resources. It is a core part of the AAA framework (authentication, authorization, accounting) and is distinct from authorization, which determines what an authenticated subject is allowed to do.

A common way to categorize authentication factors is by what the user provides: something you know (passwords or PINs), something you have (security tokens, smart cards, mobile devices used as tokens), something you are (biometrics such as fingerprints or facial recognition). Some approaches add environmental or behavioral factors, such as location, typing patterns, or movement. Many systems use multiple factors in combination, known as multi-factor authentication (MFA), to improve security.

Authentication workflows may involve password submission, challenge-response tests, biometric scans, or cryptographic proofs. Modern trends include passwordless methods that rely on devices or biometrics, and federated identity systems that rely on a trusted identity provider to authenticate users across services.

Protocols and technologies commonly used for authentication include SAML, OpenID Connect, and OAuth in federated and delegated scenarios; Kerberos in enterprise networks; and TLS with client certificates for strong transport-layer authentication. Public key infrastructure (PKI) underpins many of these mechanisms.

Security considerations include the risk of credential theft, phishing, and credential stuffing. Defenses emphasize MFA, phishing-resistant authenticators (such as FIDO2/WebAuthn), device binding, security logging and anomaly detection, and the use of passwordless options where appropriate. Password managers and good onboarding practices support usable yet secure authentication, while privacy and accessibility concerns should be addressed in system design.