Introduction:

Node.js provides an ideal environment to create server-side applications, with the possibility to employ different authentication strategies. One of the powerful tools you can use is Auth0, a flexible, drop-in solution to add authentication and authorization services to your applications. This blog will explore advanced usage of Auth0 with Node.js.

Prerequisites:

1. Basic knowledge of Node.js and Express.js
2. Familiarity with Auth0
3. An Auth0 account

Creating a Node.js Application:

Create a new directory for your application and initialize it with a package.json file. This can be done by running the following commands:

mkdir myAuthApp && cd myAuthApp
npm init -y

Setting Up Auth0:

Sign up or log into your Auth0 account. Create a new 'Regular Web Application' and note down your 'Domain', 'Client ID', and 'Client Secret'. These values will be used later.

Implementing Auth0 in Node.js:

Install necessary packages by running: npm install express dotenv passport passport-auth0 express-session.

Create a .env file and add the following lines, replacing the placeholders with the credentials from Auth0.

AUTH0_CLIENT_ID=YOUR_CLIENT_ID
AUTH0_DOMAIN=YOUR_DOMAIN
AUTH0_CLIENT_SECRET=YOUR_CLIENT_SECRET
AUTH0_CALLBACK_URL=http://localhost:3000/callback
SESSION_SECRET=YOUR_RANDOM_VALUE

Configuring Passport:

Passport is the authentication middleware for Node.js. Passport-Auth0 strategy is employed for the Auth0 implementation. Set up passport with Auth0 strategy like this:

const passport = require('passport');
const Auth0Strategy = require('passport-auth0');

let strategy = new Auth0Strategy(
  {
    domain: process.env.AUTH0_DOMAIN,
    clientID: process.env.AUTH0_CLIENT_ID,
    clientSecret: process.env.AUTH0_CLIENT_SECRET,
    callbackURL: process.env.AUTH0_CALLBACK_URL || 'http://localhost:3000/callback'
  },
  function(accessToken, refreshToken, extraParams, profile, done) {
    return done(null, profile);
  }
);

passport.use(strategy);

passport.serializeUser(function(user, done) {
  done(null, user);
});

passport.deserializeUser(function(user, done) {
  done(null, user);
});

Securing Routes:

To secure routes, you can use the 'ensureLoggedIn' middleware from 'connect-ensure-login' package. It will redirect unauthenticated users to the login page.

const ensureLoggedIn = require('connect-ensure-login').ensureLoggedIn();
app.get('/user', ensureLoggedIn, (req, res) => {
    res.send(req.user);
});

Conclusion:

Auth0 offers a robust, highly customizable authentication and authorization service. It's easy to integrate with a Node.js application and can take a lot of the work off your shoulders when it comes to managing user authentication. The above guide gives a glimpse into the advanced application of Auth0. Always remember to keep your sensitive data secure and never expose your secrets in the client-side or public repositories.