Auth0 Flask

Use when adding login, logout, and user profile to a Flask web application using session-based authentication - integrates auth0-server-python for server-rendered apps with login/callback/profile/logout flows.

Auth0 Flask Web App Integration

Add login, logout, and user profile to a Flask web application using auth0-server-python.

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Prerequisites

• Flask application
• Auth0 Regular Web Application configured (not an API — must be an Application)
• If you don't have Auth0 set up yet, use the auth0-quickstart skill first

When NOT to Use

• Python APIs with JWT Bearer validation — Use auth0-fastapi-api for FastAPI, or see the Django REST Framework quickstart
• FastAPI web app with login/logout UI — No dedicated skill yet; see the FastAPI quickstart
• Single Page Applications — Use auth0-react, auth0-vue, or auth0-angular for client-side auth
• Next.js applications — Use auth0-nextjs which handles both client and server
• Node.js web apps — Use auth0-express or auth0-fastify for session-based auth

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Quick Start Workflow

1. Install SDK

bash

pip install auth0-server-python "flask[async]" python-dotenv

Critical: You must install flask[async] (not just flask). The [async] extra installs asgiref which is required for Flask 2.0+ to support async def route handlers. Without it, async routes will not work. In requirements.txt, use flask[async]>=2.0.0.

2. Configure Environment

Create .env:

bash

AUTH0_DOMAIN=your-tenant.us.auth0.com
AUTH0_CLIENT_ID=your_client_id
AUTH0_CLIENT_SECRET=your_client_secret
AUTH0_SECRET=your_generated_app_secret
AUTH0_REDIRECT_URI=http://localhost:5000/callback

AUTH0_DOMAIN is your Auth0 tenant domain (without https://). AUTH0_CLIENT_ID and AUTH0_CLIENT_SECRET come from your Auth0 Application settings. AUTH0_SECRET is used for encrypting session data — generate with openssl rand -hex 64.

3. Configure Auth0 Dashboard

In your Auth0 Application settings:

• Allowed Callback URLs: http://localhost:5000/callback
• Allowed Logout URLs: http://localhost:5000

4. Create Auth Module

Create auth.py to initialize the ServerClient with Flask session-based stores. The stores use Flask's built-in session (cookie-based by default) for a stateless setup — no external database needed:

python

import os
from flask import session as flask_session
from auth0_server_python.auth_server.server_client import ServerClient
from auth0_server_python.auth_types import StateData, TransactionData
from auth0_server_python.store import StateStore, TransactionStore
from dotenv import load_dotenv

load_dotenv()  # Uses .env by default; pass load_dotenv(".env.local") if credentials are in .env.local


class FlaskSessionStateStore(StateStore):
    """State store that uses Flask's session for persistence."""

    def __init__(self, secret: str):
        super().__init__({"secret": secret})

    async def set(self, identifier, state, remove_if_expires=False, options=None):
        data = state.dict() if hasattr(state, "dict") else state
        flask_session[identifier] = self.encrypt(identifier, data)

    async def get(self, identifier, options=None):
        data = flask_session.get(identifier)
        if data is None:
            return None
        decrypted = self.decrypt(identifier, data)
        # Ensure to not return a dict, as the underlying SDK expects a StateData instance, not a dict
        return StateData(**decrypted) if isinstance(decrypted, dict) else decrypted

    async def delete(self, identifier, options=None):
        flask_session.pop(identifier, None)

    async def delete_by_logout_token(self, claims, options=None):
        pass


class FlaskSessionTransactionStore(TransactionStore):
    """Transaction store that uses Flask's session for persistence."""

    def __init__(self, secret: str):
        super().__init__({"secret": secret})

    async def set(self, identifier, state, remove_if_expires=False, options=None):
        data = state.dict() if hasattr(state, "dict") else state
        flask_session[identifier] = self.encrypt(identifier, data)

    async def get(self, identifier, options=None):
        data = flask_session.get(identifier)
        if data is None:
            return None
        decrypted = self.decrypt(identifier, data)
        # Ensure to not return a dict, as the underlying SDK expects a TransactionData instance, not a dict
        return TransactionData(**decrypted) if isinstance(decrypted, dict) else decrypted

    async def delete(self, identifier, options=None):
        flask_session.pop(identifier, None)


secret = os.getenv("AUTH0_SECRET")

auth0 = ServerClient(
    domain=os.getenv("AUTH0_DOMAIN"),
    client_id=os.getenv("AUTH0_CLIENT_ID"),
    client_secret=os.getenv("AUTH0_CLIENT_SECRET"),
    secret=secret,
    redirect_uri=os.getenv("AUTH0_REDIRECT_URI"),
    state_store=FlaskSessionStateStore(secret=secret),
    transaction_store=FlaskSessionTransactionStore(secret=secret),
    authorization_params={"scope": "openid profile email"},
)

Create one ServerClient instance and reuse it. Never hardcode credentials — always use environment variables.

How this works: Flask's default session is cookie-based (stateless). The SDK encrypts session data (tokens, user profile) with JWE before storing it in the session, so data is both signed and encrypted in the cookie. No server-side database is required.

No store_options or before_request needed: The SDK supports passing store_options (e.g. request/response objects) to store methods. Since these stores use flask.session — which is globally available during a request — they don't need anything from store_options, so you can call SDK methods without passing it. If you implement a custom store that manages cookies directly (instead of using flask.session), you would need to reintroduce store_options with {"request": request, "response": response}.

Cookie size note: Stateless sessions store all data in a cookie (~4KB limit). For most apps this is sufficient. If you store large amounts of session data or hit cookie size limits, switch to stateful setup.

5. Configure Flask App

In app.py, set up Flask with the secret key and session configuration:

python

import os
from flask import Flask, redirect, request
from auth import auth0
from dotenv import load_dotenv

load_dotenv()

app = Flask(__name__)
app.secret_key = os.getenv("AUTH0_SECRET")
app.config.update(
    SESSION_COOKIE_SECURE=False,  # Set to True in production (requires HTTPS)
    SESSION_COOKIE_HTTPONLY=True,
    SESSION_COOKIE_SAMESITE="Lax",
)

Critical: app.secret_key must be set for Flask session management. Without it, sessions won't work.

For production: Set SESSION_COOKIE_SECURE=True when deploying with HTTPS. Leaving it as False in production allows session cookies to be sent over unencrypted connections.

6. Add Home Route

python

@app.route("/")
async def home():
    user = await auth0.get_user()
    if user:
        return f"Hello, {user['name']}! <a href='/profile'>Profile</a> | <a href='/logout'>Logout</a>"
    return "Welcome! <a href='/login'>Login</a>"

7. Add Login Route

python

@app.route("/login")
async def login():
    authorization_url = await auth0.start_interactive_login()
    return redirect(authorization_url)

start_interactive_login() returns a URL string pointing to Auth0's Universal Login page. You must wrap it in redirect(). Authorization params (scope, redirect_uri) are already configured on the ServerClient.

8. Add Callback Route

python

@app.route("/callback")
async def callback():
    try:
        await auth0.complete_interactive_login(str(request.url))
        return redirect("/")
    except Exception as e:
        return f"Authentication error: {str(e)}", 400

Pass str(request.url) as the first argument — this is the full callback URL including the authorization code query parameters. Always wrap in try/except since the token exchange can fail (e.g. expired code, CSRF mismatch).

9. Add Profile Route (Protected)

python

@app.route("/profile")
async def profile():
    user = await auth0.get_user()
    if user is None:
        return redirect("/login")
    return (
        f"<h1>{user['name']}</h1>"
        f"<p>Email: {user['email']}</p>"
        f"<img src='{user['picture']}' alt='{user['name']}' width='100' />"
        f"<p><a href='/logout'>Logout</a></p>"
    )

get_user() returns the user's profile from the session, or None if not logged in.

10. Add Logout Route

python

@app.route("/logout")
async def logout():
    url = await auth0.logout()
    return redirect(url)

logout() returns the Auth0 logout URL. Redirect the user to it.

11. Test the App

bash

flask run

Visit http://localhost:5000/login to start the login flow.

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Stateful Setup with Redis

For production apps or when session data exceeds cookie size limits, use Flask-Session with Redis to store sessions server-side. Only a session ID is stored in the cookie.

1. Install Dependencies

bash

pip install flask-session redis

2. Configure Flask-Session

Update app.py to use Redis-backed sessions:

python

import os
from flask import Flask, redirect, request
from flask_session import Session
from auth import auth0
from dotenv import load_dotenv

load_dotenv()

app = Flask(__name__)
app.secret_key = os.getenv("AUTH0_SECRET")
app.config.update(
    SESSION_TYPE="redis",
    SESSION_PERMANENT=True,
    SESSION_KEY_PREFIX="auth0:",
    SESSION_COOKIE_SECURE=False,
    SESSION_COOKIE_HTTPONLY=True,
    SESSION_COOKIE_SAMESITE="Lax",
)
Session(app)

3. No Store Changes Needed

The same FlaskSessionStateStore and FlaskSessionTransactionStore from auth.py work without modification. Flask-Session transparently switches the flask.session backend from cookies to Redis — the stores continue to use flask.session as before.

Routes are identical to the stateless setup — no code changes needed.

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Common Mistakes

Mistake	Fix
Hardcoding domain, client_id, or client_secret in source	Always read from environment variables — never embed credentials in code
Using Authlib or python-jose directly	Not needed; auth0-server-python handles all OAuth/OIDC flows
Using Flask-Login or Flask-Dance	Not needed; the SDK manages sessions and authentication
Manually parsing JWTs with jwt.decode()	The SDK handles token validation internally
Installing flask without [async] extra	Must use flask[async]>=2.0.0 in requirements.txt — without it, async route handlers silently fail
Using synchronous route handlers	All routes calling SDK methods must be async def and use await
Forgetting app.secret_key	Required for Flask session management — without it, sessions silently fail
Using auth0-fastapi-api in Flask	That package is for FastAPI APIs — use auth0-server-python for Flask
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
Not configuring callback URL in Auth0 Dashboard	Must add http://localhost:5000/callback to Allowed Callback URLs
Returning start_interactive_login() directly	It returns a URL string, not a response — must wrap in redirect()
Not handling errors in /callback	complete_interactive_login() can fail — always wrap in try/except
Calling SDK methods without await	All SDK methods are async — forgetting await returns a coroutine instead of the result
Passing options positionally to logout()	Use logout(store_options=...) — the first positional parameter is LogoutOptions, not store options
Expecting backchannel logout to work	Not supported with cookie-based sessions — delete_by_logout_token is a no-op. Use standard /logout route
Deploying with SESSION_COOKIE_SECURE=False	Must set to True in production — cookies are sent over HTTP otherwise

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Key SDK Methods

All methods are async:

Method	Signature	Purpose
start_interactive_login	await auth0.start_interactive_login()	Returns authorization URL string — wrap in redirect()
complete_interactive_login	await auth0.complete_interactive_login(str(request.url))	Processes the callback URL, exchanges code for tokens
get_user	await auth0.get_user()	Returns current session user dict or None
get_access_token	await auth0.get_access_token()	Returns the access token for calling external APIs
logout	await auth0.logout()	Returns Auth0 logout URL string

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Related Skills

• auth0-express — For server-rendered Express web apps with login/logout sessions
• auth0-fastify — For Fastify web applications with session-based auth
• auth0-cli — Manage Auth0 resources from the terminal

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Quick Reference

ServerClient configuration:

python

auth0 = ServerClient(
    domain=os.getenv("AUTH0_DOMAIN"),                    # required
    client_id=os.getenv("AUTH0_CLIENT_ID"),              # required
    client_secret=os.getenv("AUTH0_CLIENT_SECRET"),      # required
    secret=os.getenv("AUTH0_SECRET"),                    # required (encryption secret)
    redirect_uri=os.getenv("AUTH0_REDIRECT_URI"),        # required
    state_store=FlaskSessionStateStore(secret=secret),   # required
    transaction_store=FlaskSessionTransactionStore(secret=secret),  # required
    authorization_params={"scope": "openid profile email"},  # recommended
)

Route protection pattern:

python

user = await auth0.get_user()
if user is None:
    return redirect("/login")

Environment variables:

• AUTH0_DOMAIN — your Auth0 tenant domain (e.g. tenant.us.auth0.com)
• AUTH0_CLIENT_ID — your Application's client ID
• AUTH0_CLIENT_SECRET — your Application's client secret
• AUTH0_SECRET — encryption and session secret key
• AUTH0_REDIRECT_URI — callback URL (e.g. http://localhost:5000/callback)

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Detailed Documentation

• Setup Guide - Automated setup scripts, environment configuration, Auth0 CLI usage
• Integration Guide - Protected routes, calling APIs, session management, error handling
• API Reference - Complete ServerClient API, configuration options, store implementation, security

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References

• auth0-server-python on PyPI
• Auth0 Flask Quickstart
• Flask Documentation