JWT Authentication, Explained by Actually Running One (No Setup)
The article explains JWT (JSON Web Token) authentication by demonstrating how to decode and test real tokens using a live sandbox environment. It highlights common vulnerabilities such as alg:none exploits and algorithm confusion between RS256 and HS256. Readers are guided through the structure, verification process, and security risks of JWTs without requiring any local setup.
- ▪A JWT is a self-contained, signed string composed of a header, payload, and signature, used for user authentication.
- ▪The article provides a live sandbox to test JWT behavior, including exploiting the alg:none vulnerability and observing server responses.
- ▪Common JWT vulnerabilities include accepting 'none' as the algorithm and confusing RS256 with HS256, both of which can lead to unauthorized access.
- ▪The server verifies JWTs by checking the signature, algorithm, expiration, and standard claims like exp and nbf before trusting the token.
- ▪Sensitive data should never be stored in JWTs since the payload is base64-encoded, not encrypted, and can be easily decoded.
Opening excerpt (first ~120 words) tap to expand
try { if(localStorage) { let currentUser = localStorage.getItem('current_user'); if (currentUser) { currentUser = JSON.parse(currentUser); if (currentUser.id === 3934879) { document.getElementById('article-show-container').classList.add('current-user-is-article-author'); } } } } catch (e) { console.error(e); } Parveen Kumari Posted on May 16 JWT Authentication, Explained by Actually Running One (No Setup) #ai #security #webdev #api Decode a real JWT, exploit alg:none in 30 seconds, and learn exactly what to test in your own auth — all in your browser against a live sandbox Most JWT tutorials show you a diagram and call it a day.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at DEV.to (Top).
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