JWT

JWT (JSON Web Token) is an open standard for creating secure, self-contained tokens that transmit authentication and authorization information between mobile apps and backend services. A JWT consists of three Base64-encoded parts—header, payload, and signature—joined by dots, creating a compact token that mobile apps can easily store and include in API requests. Unlike session-based authentication that requires server-side storage, JWTs contain all necessary information within the token itself, making them ideal for stateless mobile architectures and microservices where backend servers don’t maintain session state.

The token’s payload carries claims about the user (identity, permissions, expiration) in JSON format, while the cryptographic signature ensures the token hasn’t been tampered with during transmission. Mobile apps typically store JWTs in secure storage (Keychain on iOS, Keystore on Android) after successful login, then include them in the Authorization header of subsequent API requests. The server validates the signature and extracts user information without querying a database, reducing latency—crucial for mobile experiences. JWTs support expiration times and refresh token patterns, enabling secure long-term authentication without requiring frequent re-login.

For mobile developers, JWTs represent the modern standard for API authentication, replacing older session-cookie approaches ill-suited to mobile environments. Most mobile backends and authentication services including Firebase, Auth0, and custom Node.js APIs use JWT-based authentication. Understanding JWT structure, secure storage, and refresh strategies is essential for implementing secure, performant authentication flows in mobile applications.