This demonstrates using Passport.js for user authentication.
The app allows you to login using built-in users (db/users.js) or login with Facebook/Twitter/etc. You can add many other social login providers easily - search for Strategies on http://passportjs.org.
The app is based on the local and Facebook examples.
To configure OAuth providers with your own app, see the provider's developer docs to create your own app, then stick your secrets in .env.
Callback URLs to use with third-party login providers end with /login/provider/return e.g. /login/twitter/return.
Note that users and sessions are just stored in memory in this example, so you'll want to add a datastore of some form.