Authenticate and generate API access tokens using Auth0 and FastAPI

In this tutorial, we will be using Auth0 to handle authentication and issue API access tokens, and FastAPI as the backend framework. Auth0 is a powerful authentication and authorization platform that allows you to implement secure authentication for your applications. FastAPI is a modern, fast (high-performance) web framework for building APIs with Python.

Before we get started with the tutorial, make sure you have Python installed on your machine. You’ll also need an Auth0 account to use their services.

Step 1: Set up Auth0

1. Sign up for an Auth0 account at https://auth0.com/signup
2. Create a new Auth0 application by clicking on the "Create Application" button. Choose "Regular Web Applications" as the application type.
3. Configure the application settings by adding the correct Callback URLs and Allowed Web Origins for your FastAPI application.
4. Once the application is created, you will be given a Domain and Client ID. Make a note of these as we will need them later.

Step 2: Install FastAPI and required dependencies

1. Install FastAPI and uvicorn using pip:

   pip install fastapi uvicorn

Step 3: Create a FastAPI app

1. Create a new Python file, for example main.py, and import the necessary modules:

   from fastapi import FastAPI

2. Initialize the FastAPI app:

   app = FastAPI()

Step 4: Set up Auth0 authentication in FastAPI

1. Install the Auth0 Python SDK using pip:

   pip install authlib

2. Add the necessary imports to the main.py file:

   from authlib.integrations.starlette_client import OAuth

3. Configure OAuth with the Auth0 settings:

   oauth = OAuth()
   oauth.register(
   name='auth0',
   client_id='YOUR_CLIENT_ID',
   client_secret='YOUR_CLIENT_SECRET',
   authorize_url='https://YOUR_DOMAIN.auth0.com/authorize',
   token_url='https://YOUR_DOMAIN.auth0.com/oauth/token',
   client_kwargs={'scope': 'openid profile email'}
   )

   Replace YOUR_DOMAIN, YOUR_CLIENT_ID, and YOUR_CLIENT_SECRET with your Auth0 domain, client ID, and client secret.

Step 5: Create a login route

1. Add a new route to handle the login functionality:

   @app.route('/login')
   async def login(request: Request):
   redirect_uri = request.url_for('auth')
   return await oauth.auth0.authorize_redirect(request, redirect_uri)

   This route will redirect the user to the Auth0 login page for authentication.

Step 6: Create a callback route

1. Add a callback route to handle the authentication callback:

   @app.route('/auth')
   async def auth(request: Request):
   token = await oauth.auth0.authorize_access_token(request)
   user = await oauth.auth0.parse_id_token(request, token)
   return {'token': token, 'user': user}

   This route will issue an access token and retrieve the user information after successful authentication.

Step 7: Run the FastAPI app

1. Run the FastAPI app using uvicorn:

   uvicorn main:app --reload

That’s it! You now have a FastAPI app set up with Auth0 authentication and API access token issuance. Users can log in using their Auth0 credentials, and the app will issue access tokens that can be used to authenticate API requests.

This tutorial provides a basic setup for authentication and token issuance. You can customize the routes and add additional functionality as needed for your application.