auth0-fastapi-api

name	auth0-fastapi-api
description	Use when securing FastAPI API endpoints with JWT Bearer token validation, scope/permission checks, or stateless auth - integrates auth0-fastapi-api for REST APIs receiving access tokens from SPAs, mobile apps, or other clients. Also handles DPoP proof-of-possession token binding. Triggers on: Auth0FastAPI, FastAPI API auth, JWT validation, require_auth, DPoP.
license	Apache-2.0
metadata	{"author":"Auth0 <[e-mail]>"}

Auth0 FastAPI API Integration

Protect FastAPI API endpoints with JWT access token validation using auth0-fastapi-api.

Note: This SDK is currently in beta. The API surface may change before the stable 1.0 release. Check PyPI for the latest version. Requires Python >= 3.9 and FastAPI >= 0.115.11.

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Prerequisites

• FastAPI application (Python 3.9+)
• Auth0 API resource configured (not an Application — must be an API)
• If you don't have Auth0 set up yet, use the auth0-quickstart skill first

When NOT to Use

• Server-rendered web applications — Use a session-based login/logout flow instead
• Single Page Applications — Use auth0-react, auth0-vue, or auth0-angular for client-side auth
• Mobile applications — Use auth0-react-native or auth0-android
• Issuing tokens — This skill is for validating access tokens, not issuing them

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Quick Start Workflow

1. Install SDK

pip install auth0-fastapi-api python-dotenv

2. Create Auth0 API

You need an API (not Application) in Auth0.

STOP — ask the user before proceeding.

Ask exactly this question and wait for their answer before doing anything else:

"How would you like to create the Auth0 API resource?

1. Automated — I'll run Auth0 CLI scripts that create the resource and write the exact values to your .env automatically.
2. Manual — You create the API yourself in the Auth0 Dashboard (or via auth0 apis create) and provide me the Domain and Audience.

Which do you prefer? (1 = Automated / 2 = Manual)"

Do NOT proceed to any setup steps until the user has answered. Do NOT default to manual.

If the user chose Automated, follow the Setup Guide for complete CLI scripts. The automated path writes .env for you — skip Step 3 below and proceed directly to Step 4.

If the user chose Manual, follow the Setup Guide (Manual Setup section) for full instructions. Then continue with Step 3 below.

Quick reference for manual API creation:

# Using Auth0 CLI
auth0 apis create \
  --name "My FastAPI API" \
  --identifier https://my-api.example.com

Or create manually in Auth0 Dashboard → Applications → APIs

3. Configure Environment

Create .env:

AUTH0_DOMAIN=your-tenant.us.auth0.com
AUTH0_AUDIENCE=https://your-api.example.com

AUTH0_DOMAIN is your Auth0 tenant domain (without https://). AUTH0_AUDIENCE is the API identifier you set when creating the API resource in Auth0.

4. Initialize Auth0

import os
from fastapi import FastAPI, Depends
from auth0_fastapi_api import Auth0FastAPI
from dotenv import load_dotenv

load_dotenv()

app = FastAPI()

auth0 = Auth0FastAPI(
    domain=os.getenv("AUTH0_DOMAIN"),
    audience=os.getenv("AUTH0_AUDIENCE"),
)

Create one Auth0FastAPI instance per application and reuse it across routes. Never hardcode the domain or audience — always use environment variables.

5. Protect Routes

# Require any valid access token
@app.get("/api/private")
async def private(claims: dict = Depends(auth0.require_auth())):
    return {"user": claims["sub"]}

# No authentication required
@app.get("/api/public")
async def public():
    return {"message": "Public endpoint"}

The require_auth() dependency validates the Bearer token, verifies the issuer and audience, and returns the decoded JWT claims.

Error responses:

• 400 invalid_request — Missing or malformed Authorization header
• 401 invalid_token — Expired token, invalid signature, wrong issuer/audience
• 403 insufficient_scope — Valid token but missing required scopes
• 500 internal_server_error — Unexpected errors

Response body format: {"detail": {"error": "...", "error_description": "..."}}

6. Protect Routes with Scope Checks

# Requires the read:messages scope
@app.get("/api/messages")
async def get_messages(claims: dict = Depends(auth0.require_auth(scopes="read:messages"))):
    return {"messages": []}

# Requires both read:data and write:data scopes
@app.post("/api/data")
async def write_data(claims: dict = Depends(auth0.require_auth(scopes=["read:data", "write:data"]))):
    return {"created": True}

require_auth(scopes=...) checks the scope claim in the JWT. All specified scopes must be present (AND logic). Missing scopes return 403.

7. Access Token Claims

The decoded JWT claims are returned directly from the dependency:

@app.get("/api/profile")
async def profile(claims: dict = Depends(auth0.require_auth())):
    return {
        "sub": claims["sub"],       # user ID
        "scope": claims.get("scope"),  # granted scopes
    }

Key claims:

• claims["sub"] — user/client ID
• claims["scope"] — space-separated granted scopes
• claims["iss"] — issuer (your Auth0 domain URL)
• claims["aud"] — audience
• claims["exp"] — expiration timestamp
• claims["iat"] — issued-at timestamp

8. Protect Routes Without Needing Claims

@app.get("/api/protected", dependencies=[Depends(auth0.require_auth())])
async def protected():
    return {"message": "You need a valid access token to see this."}

9. Test the API

# No token — expect 401
curl http://localhost:8000/api/private

# With a valid access token
curl http://localhost:8000/api/private \
  -H "Authorization: Bearer YOUR_ACCESS_TOKEN"

Get a test token via Client Credentials flow or Auth0 Dashboard → APIs → Test tab.

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Common Mistakes

Mistake	Fix
Hardcoding domain or audience in source	Always read from environment variables — never embed credentials in code
Using python-jose or PyJWT directly	Not needed; auth0-fastapi-api handles all validation via JWKS
Manually parsing Authorization header	The SDK extracts and validates the token automatically
Calling jwt.decode() manually	The SDK verifies tokens against the JWKS endpoint — do not verify yourself
Using fastapi-users for Auth0 JWT validation	That package is for user management, not Auth0 JWT verification
Created an Application instead of an API in Auth0	Must create an API resource (Applications → APIs) — an Application doesn't issue access tokens with the right audience
Passing domain as full URL with https://	domain should be the bare domain, e.g. my-tenant.us.auth0.com, not https://my-tenant.us.auth0.com
Using an ID token instead of an access token	Must use the access token for API auth — ID tokens are for the client app, not for API authorization
Not configuring CORS for SPA clients	Add CORSMiddleware to allow requests from your frontend origin
os.getenv() returns None silently	Ensure python-dotenv is installed and load_dotenv() is called before Auth0FastAPI() initialization — or use os.environ[] to fail fast

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DPoP Support

Built-in proof-of-possession token binding per RFC 9449. DPoP is enabled by default in mixed mode (accepts both Bearer and DPoP tokens). See Integration Guide for configuration.

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Related Skills

• auth0-quickstart - Basic Auth0 setup and framework detection
• auth0-mfa - Add Multi-Factor Authentication

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Quick Reference

Auth0FastAPI configuration:

auth0 = Auth0FastAPI(
    domain=os.getenv("AUTH0_DOMAIN"),       # required (or use domains)
    audience=os.getenv("AUTH0_AUDIENCE"),    # required
    dpop_enabled=True,                       # default; set False for Bearer-only
    dpop_required=False,                     # default; set True to reject Bearer tokens
)

Route protection:

Depends(auth0.require_auth())                    # any valid token
Depends(auth0.require_auth(scopes="read:res"))   # single scope
Depends(auth0.require_auth(scopes=["r", "w"]))   # all scopes required

Accessing claims:

claims["sub"]           # user/client ID
claims["scope"]         # space-separated scopes

Environment variables:

• AUTH0_DOMAIN — your Auth0 tenant domain (e.g. tenant.us.auth0.com)
• AUTH0_AUDIENCE — your API identifier (e.g. https://api.example.com)

Common Use Cases:

• Protect routes → Depends(auth0.require_auth()) (see Step 5)
• Scope enforcement → Depends(auth0.require_auth(scopes="...")) (see Step 6)
• DPoP token binding → Integration Guide
• Reverse proxy setup → Integration Guide
• Advanced configuration → API Reference

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Detailed Documentation

• Setup Guide — Auth0 CLI setup, environment configuration, getting test tokens
• Integration Guide — DPoP, scopes, error handling, reverse proxy, testing
• API Reference — Complete constructor options, method signatures, error codes

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References

• auth0-fastapi-api GitHub
• auth0-fastapi-api on PyPI
• Auth0 FastAPI API Quickstart
• FastAPI Dependency Injection
• Access Tokens Guide