Authentication
Definition
The process of verifying that a principal (user, device, service) is who it claims to be. Distinct from authorization (what the principal is allowed to do).
Three factors
- Something you know — password, PIN
- Something you have — token, smart card, phone
- Something you are — biometric
MFA combines two or more.
Where it appears
🌐 Networking
- 802.1X — port-based authentication at L2; supplicant ↔ authenticator ↔ authentication server
- RADIUS / TACACS+ — centralized AAA for network devices
- Pre-shared keys — WPA2-PSK, IPsec PSK
🐧 Linux
- PAM — pluggable authentication modules
- SSH — public key, password, MFA via PAM
- sudo — reuses PAM
☁️ Cloud
- AWS IAM — users, roles, access keys, MFA,
AssumeRole - Azure Entra ID — managed identities, conditional access, service principals
- Instance metadata service (IMDS) — implicit machine authentication
📦 Containers
- Kubernetes ServiceAccount tokens — pod-to-API authentication
- mTLS — service-to-service inside a mesh
🔄 CI/CD
- OIDC federation — GitHub Actions → AWS/Azure without long-lived keys
- Deploy keys / PATs — repo-level access
🔐 Cybersecurity
- Zero Trust — never trust, always verify
- Kerberos — ticket-based enterprise authentication
- SAML / OIDC / OAuth — federated identity