Secure API Design: Tokens, Roles, and Scopes

APIs stay secure when they rely on tokens rather than user names. A token proves who is calling the API and what they are allowed to do. Roles group users or services by duty, while scopes limit each call to a specific action or resource.

Tokens are issued by an authorization server after proper checks. Each API request carries the token, and the API validates it, checks its issuer (iss), audience (aud), and expiration (exp). The endpoint then confirms required scopes and, where needed, a user or service role.

Tokens come in different forms. JSON Web Tokens (JWT) are self-contained and easy to inspect, while opaque tokens rely on the auth server to translate them. Choose based on your needs: JWTs are convenient for stateless validation, but opaque tokens can hide internal details and simplify revocation.

Roles and scopes create a clean access map. A role defines a collection of permissions; a scope tags a permission to a token. Endpoints can require a combination, such as read:messages with a user having the reader role, or admin-level actions restricted to a higher role.

Design tips:

  • Define a small, explicit set of roles and scopes.
  • Issue short-lived access tokens (often minutes) and use refresh tokens to renew them.
  • Validate tokens on every API call: signature, issuer, audience, and expiration.
  • Enforce least privilege: a client should get only the scopes it needs.
  • Separate authentication from authorization: use an auth server to issue tokens, and check them at the API edge and in the service.

Practical flow example: A mobile app signs in with an auth server, receives a token with scopes read:messages and write:messages. The API first validates the token, then checks that the requested action matches one of the token’s scopes before returning data. A server admin requests an admin scope for sensitive operations, which the API will refuse if the role does not allow it.

Common pitfalls to avoid: overly broad tokens, missing audience checks, no revocation, long-lived tokens, or skipping role checks on critical endpoints.

Putting it together: Start with a clear permission model, use a trusted auth server, and enforce checks consistently across all APIs.

Key Takeaways

  • Use tokens to grant precise, auditable access without sharing user credentials.
  • Pair roles with scopes to control who can do what, and where.
  • Validate tokens at every step and keep lifetimes short to reduce risk.