JSON Web Tokens and OAuth in API Security

JSON Web Tokens and OAuth are two common tools for protecting APIs. OAuth 2.0 provides a way to authorize access, while JWT is a compact token format that can carry identity and permission data. Used together, they help apps prove who they are and what they can do, without sending passwords on every request.

In a typical setup, an OAuth 2.0 server issues an access token after the client proves its identity. That token is often a JWT, signed with a private key. The resource server can verify the signature with a public key and read the claims, such as the user id, the allowed scopes, and the token’s expiry.

Key claims to check include iss (issuer), aud (audience), exp (expiration), iat (issued at), and scope. A common pattern is to keep access tokens short lived (minutes) and to use a refresh token to obtain a new one. For public clients, PKCE adds protection against code interception.

Choosing the right signing method matters. RS256, which uses a private/public key pair, is safer for multi-service environments because keys can rotate without sharing secrets. HS256, based on a shared secret, works for small teams but requires careful secret management.

Protect the token in transit and at rest. Always use HTTPS. On web apps, consider storing the access token in memory and the refresh token in a secure, httpOnly cookie. Use audience and issuer checks to avoid tokens from other systems being accepted. For stronger security, validate the token against a JWKS endpoint to fetch current public keys.

Implement scopes and roles to limit what a token can do. Revoke tokens when a user logs out or changes roles. Monitor for unusual patterns such as token reuse or very long-lived tokens.

A practical flow: a client opens the consent screen, receives an authorization code, exchanges it for tokens, then calls an API with Authorization: Bearer . If the token is valid, the API responds with data; if not, it returns 401 or 403.

This approach keeps credentials safe and gives you control over access, rotation, and revocation. It also scales as services grow, supporting teams and partners with clear boundaries.

Example JWT header: {“alg”:“RS256”,“typ”:“JWT”} while the payload carries iss, aud, exp, and scopes in a real system. Treat tokens as sensitive data and manage them as part of your security posture.

Key Takeaways

  • JWTs are a compact token format often used as access tokens in OAuth flows.
  • Always validate signature, issuer, audience, and expiration; rotate keys and use PKCE for public clients.
  • Use short-lived access tokens with refresh tokens, secure storage, and proper transport protection.