Redirecting users if they aren't using specific domain

Question

I'm trying to redirect users to a route using res.redirect, or send a file using res.send if they attempt to login using a domain other than the one specified. The condition checking is working, but I'm trying to use res.sendFile/res.redirect but it doesn't seem to be working within the scope of this function. It's clear that there isn't a res in this function, but that's all that I've come up with. Had a really good search online but I'm yet to resolve the problem.

Any help is appreciated.

passport.use(
  new GoogleStrategy({
    callbackURL: '/google/redirect',
    clientID: keys.google.clientID,
    clientSecret: keys.google.clientSecret
}, function (accessToken, refreshToken, profile, done){
  if (profile._json.hd === "HIDDEN-DOMAIN.COM") {
    User.findOne({googleId : profile.id})
  .then(function(currentUser){
    if(currentUser){
      console.log('User with ID' + currentUser.googleId +' already exists. No new entry was made');
      done(null, currentUser);
    } else {
      new User({
        username: profile.displayName,
        googleId: profile.id
      })
      .save()
      .then(function(newUser){
        console.log('New user created: ' + newUser);
        done(null, newUser);
      });
    }
  })
} else {
  console.log(__dirname);
  res.sendFile('../login.html');
};
}));

Answer 1

Use a middleware to perform the check, and next() if it passes. Checkout: https://expressjs.com/en/guide/using-middleware.html

This example shows a middleware function mounted on the / path. The function is executed for any type of HTTP request on the / path.

This example shows a route and its handler function (middleware system). The function handles GET requests.

app.use('/', function (req, res, next) {
  // Check 1
  console.log('Request URL:', req.originalUrl)
  next()
}, function (req, res, next) {
  // Check 2: Pass first check
  console.log('Request Type:', req.method)
  next()
})
app.get('/', (req, res) => {
   // Final Route
});

Example:

app.use('/first', function (req, res, next) {
    passport.use(
        new GoogleStrategy({
            callbackURL: '/google/redirect',
            clientID: keys.google.clientID,
            clientSecret: keys.google.clientSecret
        }, function (accessToken, refreshToken, profile, done){
            if (profile._json.hd === "HIDDEN-DOMAIN.COM") {
                User.findOne({googleId : profile.id})
                    .then(function(currentUser){
                        if(currentUser){
                            console.log('User with ID' + currentUser.googleId +' already exists. No new entry was made');
                            done(null, currentUser);
                        } else {
                            new User({
                                username: profile.displayName,
                                googleId: profile.id
                            })
                                .save()
                                .then(function(newUser){
                                    console.log('New user created: ' + newUser);
                                    done(null, newUser);
                                    next(); // next();
                                });
                        }
                    })
            } else {
                console.log(__dirname);
                next(); // next();
            }
        }));

}, function (req, res, next) {
    // More checks
    next()
});

app('/', (req, res) => {
    // final route here
    res.sendFile('../login.html');
})