How would you design an API authentication system using OAuth 2.0 and JWT, and what are the trade-offs between using access tokens and refresh tokens?

In depth

In designing an API authentication system using OAuth 2.0 and JWT, I would opt for OAuth 2.0 as it provides a robust framework for handling different authorization scenarios, such as authorization code flow for web applications and client credentials flow for server-to-server communication. JWTs are beneficial for stateless authentication because they encode user claims and permissions, reducing the need for database lookups on each request.

The trade-offs between using access tokens and refresh tokens are crucial. Access tokens are short-lived, which enhances security, but this can lead to user inconvenience if they expire frequently. Refresh tokens, on the other hand, allow for obtaining new access tokens without requiring the user to log in again, thus improving user experience. However, if refresh tokens are compromised, the attacker gains extended access until the token is revoked. Therefore, securing refresh tokens is paramount through measures such as secure storage and implementing additional checks during issuance and renewal.

Example scenario

In a previous project, we implemented an API for a mobile application where users could log in using OAuth 2.0. The application received an access token and a refresh token upon successful authentication. The access token was valid for 15 minutes, while the refresh token was valid for one week. We ensured that the refresh token was stored in a secure location on the device to prevent unauthorized access. This setup allowed our users to remain logged in without frequent interruptions while maintaining a strong security posture.

Common mistakes

One common mistake is over-reliance on access tokens without a proper refresh token strategy. When access tokens are short-lived, users may face frequent interruptions, creating a poor experience. Another mistake is failing to adequately secure refresh tokens, which can lead to prolonged unauthorized access if they are exposed. Developers sometimes underestimate the importance of token scopes and permissions, leading to overly permissive access that can jeopardize system security.

Follow-up questions

• What steps would you take to secure refresh tokens?
• How would you handle token revocation efficiently?
• Can you describe a scenario where a different method of authentication might be more appropriate?
• How do you ensure that JWTs are signed correctly?

Related concepts: token revocation, secure storage, authorization flows, user experience, stateless authentication