Engineering · December 2024
How to audit third-party JWT libraries
Before you adopt a JWT dependency, confirm it enforces safe defaults and handles key rotation gracefully. This checklist guides your evaluation.
1. Algorithm agility
- Does the library default to strong algorithms?
- Can you restrict allowed algorithms via configuration?
- Does it prevent downgrade attacks?
2. Key management
- Verify support for JWKS rotation with caching and expiry.
- Ensure keys are fetched over TLS and pinned where possible.
- Check for fallbacks that accept unsigned tokens.
3. Error handling
- Make sure the library differentiates between expired and invalid signatures.
- Inspect logs to avoid leaking token contents.
- Confirm exceptions bubble up so your API can deny access.
Pro tip
Run library tests against malicious fixtures: tokens with swapped headers, altered payloads, and invalid Base64 segments. JWTSecrets provides a fixture pack for enterprise customers.