api-jwt-authenticator
Secure FastAPI APIs with JWT Auth
FastAPI teams need consistent JWT authentication that protects private endpoints without leaking sensitive details. This skill guides token validation, access control, error handling, and testing for secure REST APIs.
Download the skill ZIP
Upload in Claude
Go to Settings → Capabilities → Skills → Upload skill
Toggle on and start using
Agent-readable resources
Use these links when an AI agent, crawler, or script needs clean context instead of reading the full page.
Test it
Using "api-jwt-authenticator". A FastAPI endpoint should allow users to read only their own profile.
Expected outcome:
The response would describe a protected route that reads the bearer token, validates required claims, compares the token subject to the requested profile owner, and returns forbidden access when they differ.
Using "api-jwt-authenticator". A team needs standard responses for failed authentication.
Expected outcome:
- Use unauthorized responses for missing, malformed, invalid, or expired tokens.
- Use forbidden responses when the token is valid but permissions are insufficient.
- Avoid returning token details, secret names, or validation internals in error messages.
Using "api-jwt-authenticator". A security reviewer wants JWT test cases.
Expected outcome:
The output would include tests for missing headers, malformed bearer tokens, expired tokens, wrong audience, wrong issuer, invalid roles, and resource ownership failures.
Security Audit
Low RiskStatic analysis flagged Markdown backticks, JWT terminology, and HTTP authentication documentation as suspicious patterns. Review found no executable code, shell invocation, prompt injection, malware behavior, or data exfiltration in SKILL.md. The skill is a conceptual security guide and is safe to publish with low residual risk.
Low Risk Issues (3)
Quality Score
What You Can Build
Protect FastAPI endpoints
Add JWT validation requirements to private API routes and reject invalid or expired tokens.
Review access control design
Check that token identity and resource ownership rules prevent users from accessing other users' data.
Plan authentication tests
Create test coverage for invalid tokens, expired tokens, role limits, and expected error responses.
Try These Prompts
Use this skill to list the JWT authentication requirements for my FastAPI API. Include required headers, claims, and error responses.
Use this skill to design JWT protection for these FastAPI routes. Identify which routes need authentication and which need role checks.
Use this skill to review my FastAPI JWT access control plan. Focus on user identity checks, resource ownership, and safe error messages.
Use this skill to create a JWT authentication test strategy for FastAPI. Cover invalid signatures, expired tokens, missing claims, and RBAC failures.
Best Practices
- Require HTTPS in production before accepting bearer tokens.
- Store signing secrets in environment variables or a secure vault.
- Validate signatures, expiration, issuer, audience, and required claims before trusting token data.
Avoid
- Do not accept tokens from query parameters for protected API calls.
- Do not log raw JWTs or signing secrets during authentication failures.
- Do not rely only on a role claim when resource ownership must also be checked.