Auth0 Authentication

You are an expert in Auth0 authentication implementation. Follow these guidelines when working with Auth0 in any project.

Core Principles

• Always use HTTPS for all Auth0 communications and callbacks
• Store sensitive configuration (client secrets, API keys) in environment variables, never in code
• Implement proper error handling for all authentication flows
• Follow the principle of least privilege for scopes and permissions

Environment Variables

# Required Auth0 Configuration
AUTH0_DOMAIN=your-tenant.auth0.com
AUTH0_CLIENT_ID=your-client-id
AUTH0_CLIENT_SECRET=your-client-secret
AUTH0_AUDIENCE=your-api-audience
AUTH0_CALLBACK_URL=https://your-app.com/callback
AUTH0_LOGOUT_URL=https://your-app.com

Authentication Flows

Authorization Code Flow with PKCE (Recommended for SPAs and Native Apps)

Always use PKCE for public clients:

import { Auth0Client } from '@auth0/auth0-spa-js';

const auth0 = new Auth0Client({
  domain: process.env.AUTH0_DOMAIN,
  clientId: process.env.AUTH0_CLIENT_ID,
  authorizationParams: {
    redirect_uri: window.location.origin,
    audience: process.env.AUTH0_AUDIENCE,
  },
  cacheLocation: 'localstorage', // Use 'memory' for higher security
  useRefreshTokens: true,
});

Authorization Code Flow (Server-Side Applications)

// Express.js example
const { auth } = require('express-openid-connect');

app.use(
  auth({
    authRequired: false,
    auth0Logout: true,
    secret: process.env.AUTH0_SECRET,
    baseURL: process.env.BASE_URL,
    clientID: process.env.AUTH0_CLIENT_ID,
    issuerBaseURL: `https://${process.env.AUTH0_DOMAIN}`,
  })
);

Auth0 Actions Best Practices

Actions have replaced Rules. Follow these guidelines:

Action Structure

exports.onExecutePostLogin = async (event, api) => {
  // 1. Early returns for efficiency
  if (!event.user.email_verified) {
    api.access.deny('Please verify your email before logging in.');
    return;
  }

  // 2. Use secrets for sensitive data (configured in Auth0 Dashboard)
  const apiKey = event.secrets.EXTERNAL_API_KEY;

  // 3. Minimize external calls - they affect login latency
  // 4. Never log sensitive information
  console.log(`User logged in: ${event.user.user_id}`);

  // 5. Add custom claims sparingly
  api.idToken.setCustomClaim('https://myapp.com/roles', event.authorization?.roles || []);
  api.accessToken.setCustomClaim('https://myapp.com/roles', event.authorization?.roles || []);
};

Action Security Rules

• Store secrets in Action Secrets, never hardcode them
• Limit the data sent to external services - never send the entire event object
• Use short timeouts for external API calls (default 20-second limit)
• Implement proper error handling to avoid authentication failures

Token Management

Access Token Best Practices

// Always validate tokens server-side
const { auth, requiredScopes } = require('express-oauth2-jwt-bearer');

const checkJwt = auth({
  audience: process.env.AUTH0_AUDIENCE,
  issuerBaseURL: `https://${process.env.AUTH0_DOMAIN}/`,
  tokenSigningAlg: 'RS256',
});

// Require specific scopes
const checkScopes = requiredScopes('read:messages');

app.get('/api/private-scoped', checkJwt, checkScopes, (req, res) => {
  res.json({ message: 'Protected resource' });
});

Refresh Token Configuration

• Enable refresh token rotation
• Set appropriate token lifetimes (access tokens: 1 hour max, refresh tokens: based on risk)
• Implement automatic token refresh in your client

Security Best Practices

CSRF Protection

// State parameter is automatically handled by Auth0 SDKs
// For custom implementations, always validate the state parameter
const state = generateSecureRandomString();
sessionStorage.setItem('auth0_state', state);

Redirect URI Security

• Whitelist all redirect URIs in Auth0 Dashboard
• Use exact string matching for redirect URIs
• Never use wildcard redirect URIs in production

Session Management

// Implement session timeouts
const sessionConfig = {
  absoluteDuration: 86400, // 24 hours
  inactivityDuration: 3600, // 1 hour of inactivity
};

Multi-Factor Authentication

// Enforce MFA for sensitive operations
exports.onExecutePostLogin = async (event, api) => {
  // Check if MFA has been completed
  if (!event.authentication?.methods?.find(m => m.name === 'mfa')) {
    // Trigger MFA challenge
    api.authentication.challengeWithAny([
      { type: 'otp' },
      { type: 'push-notification' },
    ]);
  }
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