JWT Token Validation Fails - Invalid Signature or Expiration
API requests fail with JWT verification errors even though the token appears valid. Tokens work initially but fail after some time or across different server instances.
Symptoms include immediate '401 Unauthorized' on API calls, 'JsonWebTokenError: invalid signature', or tokens expiring immediately after issue.
Error Messages You Might See
Common Causes
- Secret key mismatch between token creation and verification
- JWT expires too quickly or has wrong expiration time
- Token created with different secret than verification uses
- Multiple server instances using different secrets
- Clock skew between client and server causing 'not yet valid' errors
How to Fix It
Store JWT secret in environment variable and use identical value for both signing and verification
Set reasonable expiration: 15min for access token, 7d for refresh token
Implement token refresh: when access token expires, use refresh token to get new one without user re-logging in
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I’m a Senior Python Developer specializing in building secure, scalable, and highly available systems. I work primarily with Python, Django, FastAPI, Docker, PostgreSQL, and modern AI tooling such as PydanticAI, focusing on clean architecture, strong design principles, and reliable DevOps practices. I enjoy solving complex engineering problems and designing systems that are maintainable, resilient, and built to scale.
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Milan Surelia
Milan Surelia is a Mobile App Developer with 5+ years of experience crafting scalable, cross-platform apps at 7Span and Meticha. At 7Span, he engineers feature-rich Flutter apps with smooth performance and modern UI. As the Co-Founder of Meticha, he builds open-source tools and developer-focused products that solve real-world problems.
Expertise:
💡 Developing cross-platform apps using Flutter, Dart, and Jetpack Compose for Android, iOS, and Web.
🖋️ Sharing insights through technical writing, blogging, and open-source contributions.
🤝 Collaborating closely with designers, PMs, and developers to build seamless mobile experiences.
Notable Achievements:
🎯 Revamped the Vepaar app into Vepaar Store & CRM with a 2x performance boost and smoother UX.
🚀 Launched Compose101 — a Jetpack Compose starter kit to speed up Android development.
🌟 Open source contributions on Github & StackOverflow for Flutter & Dart
🎖️ Worked on improving app performance and user experience with smart solutions.
Milan is always happy to connect, work on new ideas, and explore the latest in technology.
You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.
Get HelpFrequently Asked Questions
What's a good JWT expiration time?
Access tokens: 15 minutes. Refresh tokens: 7 days. This balances security with user experience
How do I implement token refresh?
Store refresh token in secure httpOnly cookie. When access token expires, send refresh token to /api/refresh endpoint to get new access token
Why does my token fail on different servers?
Ensure all server instances use the same JWT secret from environment variables