Benefits and Drawbacks of JWTs

This comprehensive guide on JSON Web Tokens (JWTs) will cover the implementation considerations, architectural trade-offs, and practical alternatives for modern applications.

JSON Web Tokens have gained significant traction, with many Customer Identity and Access Management (CIAM) platforms promoting them as a universal authentication solution. While JWTs offer compelling advantages, understanding their limitations is crucial for making informed architectural decisions.

From a technical standpoint, JWTs function as self-contained identity containers. They encapsulate user identity data in JSON format and can be distributed across distributed systems and microservices. The key architectural advantage is that any service can independently validate a JWT without making network calls to the issuing identity provider. Once validation succeeds, the service can extract user claims and authorization data directly from the token payload.

Here's how the JWT workflow operates in a distributed architecture:

Compare this to opaque tokens (also called reference tokens), which are essentially random strings containing no embedded data. These tokens require a round-trip API call to the identity provider for validation and user data retrieval.

The opaque token validation flow looks like this:

This validation pattern introduces network latency and requires the identity provider to maintain token state in persistent storage. JWTs eliminate both the network overhead and storage requirements by being stateless and self-validating.

However, several technical considerations can impact your implementation decision. Let's examine the key factors one should evaluate.

Fixed Expiration Windows vs. Sliding Sessions

JWTs implement absolute expiration times (using the exp claim). Unlike traditional server-side sessions that extend based on user activity, JWTs maintain fixed lifespans regardless of user interactions. This fundamental difference affects session management patterns.

In traditional session-based applications, user activity triggers session extension - clicking a button or making an API call resets the inactivity timer. This sliding window approach aligns with typical user experience expectations where active users remain authenticated.

JWTs require explicit token renewal through programmatic replacement. When a JWT approaches expiration, your application must request a new token rather than extending the existing one. This pattern necessitates implementing refresh token mechanisms.

Refresh tokens solve the renewal challenge but introduce complexity. These are typically opaque tokens stored server-side that can generate new JWTs. Refresh tokens can implement flexible expiration policies (including sliding windows) because they're managed by the identity provider rather than being self-contained like JWTs.

Cryptographic Overhead and Performance Implications

JWT validation requires cryptographic signature verification, which introduces computational overhead compared to simple database lookups used with session IDs or opaque tokens.

The JWT structure consists of three Base64-encoded segments:

It's also important to note that performance characteristics vary significantly based on the signing algorithm, for e.g. for JSON Serialization + Base64 Encoding has a throughput of 400,000/s, while for JSON Serialization + Base64 Encoding + RSA Signing has a throughput of 200/s.

• HMAC (Symmetric) Signing: Performant than RSA but requires sharing the secret key across all validating services. This creates security concerns since any service with the key can forge tokens. It's best suited for internal microservices within a trusted network boundary.

• RSA (Asymmetric) Signing: More secure than HMAC through public/private key pairs. Services only need the public key for validation, preventing token forgery. However, RSA operations are computationally expensive, potentially creating bottlenecks in high-throughput applications.

Consider implementing JWT caching strategies or connection pooling for validation services to mitigate performance impacts in production environments.

Token Revocation Challenges

JWTs present a significant architectural challenge: immediate revocation is not straightforward. Since tokens are self-contained and validated independently, there's no central authority to consult for revocation status.

This creates scenarios where valid JWTs continue working even after:

• User account suspension or deletion
• Password changes requiring re-authentication
• Administrative security actions
• Role or permission modifications

Several mitigation strategies exist:

• Short-lived JWTs with Refresh Tokens: Use brief JWT lifespans (5-15 minutes) combined with refresh token revocation
• Block JWTs with Caching: Maintain revoked token lists in a distributed cache (like Redis)
• Webhook-based Revocation Events: Implement real-time revocation notifications across services

Security Vulnerabilities and Implementation Pitfalls

While not inherent flaws in the JWT specification, several common implementation mistakes create security vulnerabilities:

• The "none" Algorithm Attack: Some JWT libraries accept tokens with alg: "none", effectively creating unsigned tokens. Attackers can modify token payloads and set the algorithm to "none" to bypass signature validation.

• Key Confusion Attacks: The kid (Key ID) header can be exploited if applications blindly load signing keys based on this value. Attackers might manipulate the kid to reference unexpected keys or files.

Prevention strategies:

• Explicitly enable allowed algorithms in your JWT validation library
• Validate the kid header against a known set of key identifiers
• Implement proper key rotation and management practices
• Regularly audit JWT validation code for security vulnerabilities

Conclusion

JWTs provide a standardized way for services to interact with user identity data across distributed systems. By encoding user information, permissions, and metadata in a self-contained, cryptographically signed format, JWTs eliminate the need for services to make database lookups or API calls to validate user sessions. This standardization means any service in your architecture can independently verify a user's identity and permissions by simply validating the JWT signature and parsing the embedded claims. While JWTs introduce complexity around token management, revocation, and performance considerations, they solve the fundamental problem of sharing authenticated user context across multiple services without requiring shared state or synchronous communication between components.