API Authentication Guide for Modern Web Apps

Modern web applications have several authentication options, each suited to different use cases. JWT tokens are popular for stateless APIs and single-page applications. OAuth 2.0 enables users to sign in with their existing accounts from providers like Google and GitHub. API keys are simple but suitable only for server-to-server communication. Session-based authentication stores state on the server and is the most traditional approach. Choosing the right method depends on your application architecture and security requirements.

JSON Web Tokens are self-contained tokens that encode user identity and claims. The server signs the token with a secret key and the client includes it in subsequent requests via the Authorization header. JWTs are stateless, meaning the server does not need to store session data. However, this also means you cannot easily revoke individual tokens. Use short expiration times with refresh token rotation to minimize the risk of token compromise. Always verify the token signature and expiration on every request.

OAuth 2.0 lets users authenticate with existing accounts from providers like Google, GitHub, Apple, and others. This improves conversion rates since users do not need to create yet another account. The OAuth flow involves redirecting users to the provider, receiving an authorization code, and exchanging it for access tokens. Use established libraries like NextAuth.js, Passport.js, or Auth0 rather than implementing OAuth flows from scratch, as the specification has many security-critical nuances.

API keys are simple tokens that identify the calling application. They are best suited for server-to-server communication where both parties are trusted. Never use API keys as the sole authentication method for user-facing applications because they cannot identify individual users. Store API keys securely, rotate them periodically, and implement key-specific rate limits. Provide your API consumers with separate keys for development and production environments.

Where you store authentication tokens significantly impacts your application's security. httpOnly cookies are the most secure option for web applications because JavaScript cannot access them, preventing XSS attacks from stealing tokens. LocalStorage is convenient but vulnerable to XSS. If you must use localStorage, implement additional protections like Content-Security-Policy headers. For mobile applications, use the platform's secure storage mechanism like Keychain on iOS or Keystore on Android.

Access tokens should have short lifetimes, typically 15 minutes to an hour. When they expire, the client uses a refresh token to obtain a new access token. Implement refresh token rotation where each use of a refresh token issues both a new access token and a new refresh token, invalidating the old refresh token. This limits the damage of a compromised refresh token. Detect refresh token reuse as a signal of potential token theft and invalidate all tokens for that user.

Implementing authentication correctly is one of the most security-critical aspects of any application. Subtle bugs in token validation, session management, or OAuth flows can expose your entire user base. AI-generated authentication code frequently contains issues like missing token validation, insecure storage, or improper refresh flows. SpringCode implements production-grade authentication systems that protect your users with battle-tested security patterns.