JWT Token Validation Failing Unexpectedly
JWT tokens are generated successfully but validation fails on subsequent requests. User logs in, receives token, but next request with the token in Authorization header is rejected. Tokens work briefly then expire or fail unexpectedly.
Token generation and validation logic both exist but something about the verification is failing.
Error Messages You Might See
Common Causes
- Secret key different between generation and validation (different environment, code change)
- Token expiration time too short or checking incorrectly
- Signature algorithm mismatch (HS256 vs RS256)
- Token claims (sub, iss, aud) don't match expectations
- Clock skew: server time different from client, causing expiration validation to fail
How to Fix It
Verify secret key is consistent. Use JWT.io to decode token and inspect claims. Check expiration claim: 'exp' is timestamp. Allow clock skew: validation can tolerate small time differences. Ensure algorithm matches: if generated with HS256, validate with HS256. Log validation failures with details: which claim failed, expected vs actual.
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Get HelpFrequently Asked Questions
How to verify JWT signature?
Use library: jwt.verify(token, secret). Library handles signature check and claim validation.
What should token expiration be?
Short-lived access tokens: 15-60 minutes. Long-lived refresh tokens: days/weeks. Set exp claim to current time + duration.
How to handle clock skew?
Allow tolerance: jwt.verify(token, secret, {clockTolerance: 30}) allows 30 seconds time difference.