OAuth callback routes and session handling with Passport

Wiring Routes

app.use(passport.initialize());
app.use(passport.session());

// Initiates OAuth redirect
app.get('/auth/google',
  passport.authenticate('google', { scope: ['profile', 'email'] })
);

// Handles the callback
app.get('/auth/google/callback',
  passport.authenticate('google', {
    failureRedirect: '/login?error=oauth_failed',
    successRedirect: '/dashboard'
  })
);

// Logout
app.post('/auth/logout', (req, res) => {
  req.logout((err) => {
    if (err) return res.status(500).end();
    res.redirect('/login');
  });
});

// Route protection
function ensureAuth(req, res, next) {
  if (req.isAuthenticated()) return next();
  res.redirect('/login');
}

app.get('/dashboard', ensureAuth, (req, res) => {
  res.json({ user: req.user });
});

Custom Callback Pattern

If you need to inspect the OAuth result before redirecting (e.g., to return a JWT instead of using session), use a custom callback instead of successRedirect. Call req.login(user, cb) manually if you want Passport to serialize the user into the session.