auth0-fastify-api
Use when protecting Fastify API endpoints with JWT Bearer token validation or scope checks. Integrates @auth0/auth0-fastify-api for stateless APIs receiving access tokens from frontends or mobile apps.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/auth0/agent-skills --skill auth0-fastify-api- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads auth0-fastify-api automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Auth0 Fastify API Integration
Protect Fastify API endpoints with JWT access token validation using @auth0/auth0-fastify-api.
Prerequisites
- Fastify API application (v5.x or newer)
- Node.js 20 LTS or newer
- Auth0 API configured (not Application - must be API resource)
- If you don't have Auth0 set up yet, use the
auth0-quickstartskill first
When NOT to Use
- Server-rendered web applications - Use
@auth0/auth0-fastifyfor session-based auth - Single Page Applications - Use
auth0-react,auth0-vue, orauth0-angularfor client-side auth - Next.js applications - Use
auth0-nextjsskill - Mobile applications - Use
auth0-react-nativefor React Native/Expo
Quick Start Workflow
1. Install SDK
npm install @auth0/auth0-fastify-api fastify dotenv
2. Create Auth0 API
You need an API (not Application) in Auth0:
# Using Auth0 CLI
auth0 apis create \
--name "My Fastify API" \
--identifier https://my-api.example.com
Or create manually in Auth0 Dashboard → Applications → APIs
3. Configure Environment
Create .env:
AUTH0_DOMAIN=your-tenant.auth0.com
AUTH0_AUDIENCE=https://my-api.example.com
4. Configure Auth Plugin
Create your Fastify server (server.js):
import 'dotenv/config';
import Fastify from 'fastify';
import fastifyAuth0Api from '@auth0/auth0-fastify-api';
const fastify = Fastify({ logger: true });
// Register Auth0 API plugin
await fastify.register(fastifyAuth0Api, {
domain: process.env.AUTH0_DOMAIN,
audience: process.env.AUTH0_AUDIENCE,
});
fastify.listen({ port: 3001 });
5. Protect Routes
// Public route - no authentication
fastify.get('/api/public', async (request, reply) => {
return {
message: 'Hello from a public endpoint!',
timestamp: new Date().toISOString(),
};
});
// Protected route - requires valid JWT
fastify.get('/api/private', {
preHandler: fastify.requireAuth()
}, async (request, reply) => {
return {
message: 'Hello from a protected endpoint!',
user: request.user.sub,
timestamp: new Date().toISOString(),
};
});
// Protected route with user info
fastify.get('/api/profile', {
preHandler: fastify.requireAuth()
}, async (request, reply) => {
return {
profile: request.user, // JWT claims
};
});
6. Test API
Test public endpoint:
curl http://localhost:3001/api/public
Test protected endpoint (requires access token):
# First, obtain an access token (e.g. via Auth0 Dashboard > APIs > Test tab)
curl http://localhost:3001/api/private \
-H "Authorization: Bearer $ACCESS_TOKEN"
Common Mistakes
| Mistake | Fix |
|---|---|
| Created Application instead of API in Auth0 | Must create API resource in Auth0 Dashboard → Applications → APIs |
| Missing Authorization header | Include Authorization: Bearer <token> in all protected endpoint requests |
| Wrong audience in token | Client must request token with matching audience parameter |
| Using ID token instead of access token | Must use access token for API auth, not ID token |
| Not handling 401/403 errors | Implement proper error handling for unauthorized/forbidden responses |
Related Skills
auth0-quickstart- Basic Auth0 setupauth0-fastify- For server-rendered Fastify web apps with sessionsauth0-mfa- Add Multi-Factor Authenticationauth0-cli- Manage Auth0 resources from the terminal
Quick Reference
Plugin Options:
domain- Auth0 tenant domain (required)audience- API identifier from Auth0 API settings (required)
Request Properties:
request.user- Decoded JWT claims objectrequest.user.sub- User ID (subject)
Middleware:
fastify.requireAuth()- Protect route with JWT validationfastify.requireAuth({ scopes: 'read:data' })- Require specific scopefastify.requireAuth({ scopes: ['read:data', 'write:data'] })- Require specific scopes
Common Use Cases:
- Protect routes → Use
preHandler: fastify.requireAuth()(see Step 5) - Get user ID →
request.user.sub - Custom claims → Access via
request.user['namespace/claim']
References
FAQ
What does the auth0-fastify-api skill do?
Use when protecting Fastify API endpoints with JWT Bearer token validation or scope checks. Integrates @auth0/auth0-fastify-api for stateless APIs receiving access tokens from frontends or mobile apps.
How do I install auth0-fastify-api?
Run npx skills add https://github.com/auth0/agent-skills --skill auth0-fastify-api in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/auth0-fastify-api/ (personal) or .claude/skills/auth0-fastify-api/ (project).
Which AI agents can use auth0-fastify-api?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is auth0-fastify-api safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains auth0-fastify-api?
It is published by auth0 in auth0/agent-skills, and it is an official skill from the maker of the technology it covers. It has 562 recorded installs.
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