How to Implement JWT Authentication Securely in Web Applications

JWT (JSON Web Token) is a compact token format used to transmit claims between parties, consisting of a header, payload, and signature — but it is not a security solution on its own. One of the most common mistakes developers make is storing JWTs in localStorage, which exposes tokens to cross-site scripting (XSS) attacks; httpOnly cookies are the safer alternative. Short-lived access tokens (around 15 minutes) should be paired with long-lived refresh tokens, also stored in httpOnly cookies, to maintain sessions without repeatedly asking users to log in. Cookie-based authentication introduces CSRF risks, which can be mitigated using the SameSite=Strict attribute or dedicated CSRF tokens. Additional best practices include using strong secrets via environment variables, always specifying allowed algorithms during verification, and accepting that JWT's stateless nature makes token revocation difficult without a blacklist.