Authentication can be implemented using libraries like passport for user login. It provides strategies for various authentication methods (e.g., local, OAuth). Example of using Passport for local authentication:
const passport = require('passport');
const LocalStrategy = require('passport-local').Strategy;
passport.use(new LocalStrategy((username, password, done) => {
// Verify user credentials
User.findOne({ username }, (err, user) => {
if (err) return done(err);
if (!user || user.password !== password) return done(null, false);
return done(null, user);
});
}));