Klientautentisering

Klientautentisering (client authentication) is the process by which a system verifies the identity of a client—an end user or a service—before allowing access to resources. It is distinct from server authentication, though in some setups both parties authenticate each other (mutual authentication).

Common methods include something the client knows (passwords, passphrases), something the client has (API keys, tokens, hardware tokens, client certificates), and something the client is (biometrics). Modern architectures often rely on tokens issued by an authorization server (OAuth 2.0, OpenID Connect) or through client certificates in TLS (mutual TLS, mTLS).

Protocols and tokens frequently used for client authentication include TLS with client certificates; OAuth 2.0 / OIDC for web and API access; SAML; and JSON Web Tokens (JWTs). These mechanisms enable different deployment models, from user-facing applications to automated service-to-service communication.

Use cases include securing web applications, APIs, microservices, VPNs, and cloud services, where clients range from browsers to automated processes. In service-to-service scenarios, strong emphasis is placed on automated credential management and token lifetimes.

Security considerations and best practices emphasize: enforcing multi-factor authentication (MFA) where feasible; protecting credentials and cryptographic keys; using short-lived tokens and proper revocation mechanisms; implementing PKI certificate management and certificate rotation; isolating service accounts with least-privilege access; and continuously monitoring and auditing authentication events.

Implementation details involve maintaining a trusted certificate authority (CA) or identity provider, managing certificate lifecycles, handling certificate revocation lists (CRLs) or OCSP, and securely storing credentials and private keys to minimize risk of leakage.