auth-implementation-patterns

OAuth 2.0 authentication delegates user identity verification to a trusted provider, then issues tokens to your application. Design the authorization flow (authorization code, implicit, or client credentials), configure redirect URIs, exchange authorization codes for access tokens, and validate tokens on each API request. This pattern is ideal for delegated authentication and third-party integrations.

Access tokens are short-lived credentials that grant immediate API access; refresh tokens are long-lived credentials used to obtain new access tokens without re-authentication. Issue access tokens with expiration (5–15 minutes) and refresh tokens with longer validity (days or weeks). Store refresh tokens securely server-side and rotate them on use to prevent token compromise.

JWT (JSON Web Token) authentication stateless verification of user identity and permissions. Sign tokens with a secret key, include claims (user ID, roles, expiration), and validate the signature on every request. Store JWTs in httpOnly cookies or secure storage, set short expiration times, and implement token refresh logic to minimize exposure if a token is stolen.

RBAC enforces authorization by mapping users to roles and roles to permissions. Define role hierarchies, assign roles during user creation or profile updates, embed roles in tokens or session data, and check permissions before executing sensitive operations. Implement policy enforcement at API endpoints, database queries, and business logic layers for defense-in-depth.

Session-based authentication stores user state server-side and issues session identifiers in cookies; token-based authentication (JWT, OAuth) is stateless and scales better for APIs and distributed systems. Session authentication is simpler for monolithic web applications; token-based is preferred for microservices, mobile apps, and multi-tenant architectures. Choose based on your deployment model and scalability requirements.

Authentication failures arise from invalid tokens, expired credentials, incorrect signatures, or missing authorization headers. Log token validation steps (signature verification, expiration checks, claim validation), inspect HTTP headers and request payloads, and test with valid and invalid tokens. Use tools like JWT decoders to inspect token contents and verify claims match expected values.