Start by clarifying the requirements and constraints, then outline a minimal architecture: an HTTP server with a single endpoint that validates Auth0-issued JWTs using RS256 and JWKS. Walk through the implementation step-by-step, emphasizing security best practices and trade-offs, and finish by discussing testing and potential extensions.
Pro tip: Demonstrate awareness of JWKS caching and key rotation, and mention that you would validate the token's issuer, audience, and expiration to prevent common JWT vulnerabilities. Also, note that you would use a well-vetted library rather than implementing JWT verification from scratch.
Ask about expected load, deployment environment, and whether the MCP server needs to support multiple tools or just one. Confirm that Auth0 is the identity provider and that tokens are RS256-signed.
Outline a simple HTTP server (e.g., using Node.js/Express, Python/Flask, or Go) with a single endpoint for the tool. Describe how the server will fetch JWKS from Auth0, cache keys, and validate incoming JWTs.
Explain the steps: extract the Bearer token, decode the header to get the key ID (kid), fetch the corresponding public key from Auth0's JWKS endpoint, verify the signature, and validate standard claims (iss, aud, exp).
Describe how to protect the tool endpoint by requiring a valid JWT. Discuss error handling for invalid/expired tokens and returning appropriate HTTP status codes (401, 403).
Mention testing with valid and invalid tokens, and discuss trade-offs like caching JWKS vs. fetching per request, using middleware vs. inline validation, and scalability considerations.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
This part was actually pretty clean once the JWT middleware was solid.
Start by clarifying the requirement: enforce a scope check before executing the whoami tool, returning 403 if the token lacks 'tool:whoami'. Then outline a middleware or decorator-based approach that extracts scopes from the validated token, checks for the required scope, and short-circuits with a 403 response. Emphasize security best practices like fail-closed behavior and avoiding scope leakage.
Pro tip: Mention that scope validation should happen after token signature and expiration validation, and that you should log authorization failures for auditing without exposing sensitive token details.
Confirm that the token is a JWT or opaque token with scopes, and that the whoami tool is an API endpoint or function. Ask about existing auth middleware and error response format.
Decide where to enforce the scope: in a middleware, decorator, or at the tool handler level. Ensure the check is centralized and reusable for other tools.
Parse the token to extract scopes (e.g., from 'scope' claim), then check if 'tool:whoami' is present. Use a constant-time comparison if needed, and fail closed if scopes are missing.
Return HTTP 403 Forbidden with a clear error message when the scope is absent. Avoid leaking whether the token is valid or not beyond the 403.
Write unit and integration tests for valid, invalid, and missing scope cases. Add logging/metrics for authorization failures to detect abuse.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Straightforward once everything else was working.
Start by clarifying that the whoami endpoint should only return claims from a validated token, never from unverified input. Then outline the validation steps (signature, issuer, audience, expiry) and map standard OIDC claims to the response fields. Finally, discuss security considerations like not exposing sensitive claims and handling errors gracefully.
Pro tip: Emphasize that the endpoint should be stateless and derive identity solely from the token, avoiding any server-side session lookup. Also mention that returning the raw token or sensitive claims like 'sub' in plain text could be a security risk if not properly protected.
Verify the token's signature, issuer, audience, and expiration using the appropriate JWKS or introspection endpoint. Reject invalid tokens with a 401 Unauthorized response.
Parse the validated token to extract standard OIDC claims: subject (sub), client ID (client_id or azp), issuer (iss), audience (aud), and scopes (scope or scp).
Structure the response as a JSON object with clear field names, e.g., { "subject": "...", "client_id": "...", "issuer": "...", "audience": "...", "scopes": ["..."] }.
Return appropriate HTTP status codes (401 for invalid token, 403 for insufficient scope) and avoid leaking sensitive information in error messages.
Ensure the endpoint is protected by authentication, and consider whether to include additional claims like email or groups based on privacy requirements.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.