Choosing Between JWKS and Token Introspection for OAuth 2.0 Token Validation

When building secure APIs or applications with OAuth 2.0, validating access tokens is a critical step. Two common approaches for token validation are JWKS (JSON Web Key Set) and the Token Introspection Specification (RFC 7662). Each has its strengths, use cases, and trade-offs. In this blog post, we’ll explore both methods, compare their pros and cons, and help you decide which is best for your system.

What Are JWKS and Token Introspection?

JWKS

• Purpose: Validates JSON Web Tokens (JWTs) locally.
• How It Works: The authorization server exposes a JWKS endpoint (e.g., /.well-known/jwks.json) containing public keys. The resource server uses these keys to verify the JWT’s signature and checks claims like expiration (exp), issuer (iss), and audience (aud).
• Key Feature: No network call is needed for validation after caching the JWKS, making it fast and decentralized.

Token Introspection (RFC 7662)

• Purpose: Validates both opaque tokens and JWTs by querying the authorization server.
• How It Works: The resource server sends the token to the authorization server’s introspection endpoint (e.g., /introspect), which returns metadata like whether the token is active, its scopes, and expiration time.
• Key Feature: Provides real-time token status, including revocation checks, but requires a network call.

Comparing JWKS and Token Introspection

Here’s a detailed comparison to guide your decision:

When to Use JWKS

Choose JWKS if:

• Your authorization server issues JWTs and provides a JWKS endpoint (e.g., Auth0, Okta, Keycloak).
• You need high performance and scalability for high-traffic APIs.
• Your system is distributed, and resource servers can validate tokens independently.
• You’re comfortable with short-lived tokens (e.g., 5–60 minutes) to reduce revocation risks.
• You can implement secure JWT validation using libraries like jsonwebtoken (Node.js), PyJWT (Python), or jjwt (Java).

JWKS Workflow

1. Fetch and cache the JWKS from https://auth-server/.well-known/jwks.json.
2. Verify the JWT’s signature using the cached public key.
3. Check claims (exp, iss, aud, etc.) for validity.
4. Refresh the JWKS periodically to handle key rotation.

Example: Auth0

Auth0 provides a JWKS endpoint at https://<your-domain>/.well-known/jwks.json. Resource servers validate JWTs locally, making it ideal for scalable APIs.

When to Use Token Introspection

Choose Token Introspection if:

• Your server issues opaque tokens that can’t be validated locally.
• You need real-time revocation checks (e.g., for financial or sensitive applications).
• Your system is centralized, and resource servers are tightly coupled with the auth server.
• You prioritize simplicity over performance.
• The authorization server supports an introspection endpoint (e.g., Google, Keycloak, Okta).
• You’re using long-lived tokens where revocation is critical.

Introspection Workflow

1. Send a POST request to the introspection endpoint:

   POST /introspect HTTP/1.1
   Host: auth-server
   Authorization: Bearer <client_credentials>
   Content-Type: application/x-www-form-urlencoded

   token=<access_token>

1. Parse the response:

   {
     "active": true,
     "scope": "read write",
     "client_id": "s6BhdRkqt3",
     "exp": 1419356238
   }

1. Cache results briefly (if allowed) to reduce network calls.

Example: Google

Google’s tokeninfo endpoint (https://www.googleapis.com/oauth2/v3/tokeninfo) validates tokens, making introspection suitable for legacy systems or revocation checks.

Can You Use Both?

Yes! A hybrid approach can combine the strengths of both:

• Use JWKS for local JWT validation to optimize performance.
• Fall back to introspection for:
  • Real-time revocation checks (e.g., for critical operations).
  • Validating tokens when JWKS fails (e.g., key rotation issues).
  • Supporting opaque tokens during a transition to JWTs.

For example, validate JWTs locally with JWKS but periodically query the introspection endpoint to confirm a token hasn’t been revoked.

Practical Tips

• Check Your OAuth Provider: Review documentation to confirm support for JWKS, introspection, or both. Most modern providers (Auth0, Okta, Keycloak) support both.
• Default to JWKS for JWTs: If JWTs are used, JWKS is faster and more scalable. Ensure robust claim validation.
• Use Introspection for Opaque Tokens: If your tokens are opaque or revocation is critical, introspection is the way to go.
• Optimize Performance:
  • For JWKS, cache the JWKS for hours/days, refreshing only when keys rotate (check kid in the JWT).
  • For introspection, cache responses briefly (if allowed) to reduce network calls.
• Security:
  • JWKS: Use HTTPS to fetch JWKS and validate the auth server’s certificate.
  • Introspection: Protect client credentials and use TLS for endpoint communication.
• Token Lifetime:
  • JWKS: Use short-lived tokens to minimize revocation needs.
  • Introspection: Longer-lived tokens are viable with real-time checks.

Real-World Examples

• Auth0: Supports JWKS for JWTs and introspection. Use JWKS for performance, introspection for revocation.
• Google: Offers JWKS and a tokeninfo endpoint. Prefer JWKS for scalability, tokeninfo for legacy needs.
• Keycloak: Provides both. Use JWKS for distributed systems, introspection for centralized setups.
• Okta: Supports both. JWKS for high-traffic APIs, introspection for real-time checks.

Decision Workflow

1. Token Type?
   • JWT: Use JWKS if a JWKS endpoint is available.
   • Opaque: Use introspection.
2. Revocation Critical?
   • Yes: Use introspection or a hybrid approach.
   • No: JWKS with short-lived tokens is sufficient.
3. Performance Needs?
   • High-traffic: Prefer JWKS.
   • Low-traffic/centralized: Introspection is simpler.
4. Provider Support?
   • If both are available, lean toward JWKS for scalability, with introspection as a fallback.

Conclusion

• JWKS is ideal for JWTs, distributed systems, and high-performance APIs. It’s fast, scalable, and reduces auth server dependency.
• Token Introspection is best for opaque tokens, real-time revocation, or centralized systems where simplicity matters.
• A hybrid approach can offer the best of both worlds for complex use cases.

Check your OAuth 2.0 provider’s documentation to confirm supported methods and endpoints. By understanding your system’s needs—token type, performance, revocation, and architecture—you can choose the right validation approach for secure and efficient token handling.