Here is one way to do this, with comments throughout. The main thing is understanding this page from the author: http://passportjs.org/guide/authenticate/, which I explain a little more in this example ...
It might be easier to read bottom to top:
var authenticate = function(req, success, failure) {
// Use the Google strategy with passport.js, but with a custom callback.
// passport.authenticate returns Connect middleware that we will use below.
//
// For reference: http://passportjs.org/guide/authenticate/
return passport.authenticate('google',
// This is the 'custom callback' part
function (err, user, info) {
if (err) {
failure(err);
}
else if (!user) {
failure("Invalid login data");
}
else {
// Here, you can do what you want to control
// access. For example, you asked to deny users
// with a specific email address:
if (user.emails[0].value === "no@emails.com") {
failure("User not allowed");
}
else {
// req.login is added by the passport.initialize()
// middleware to manage login state. We need
// to call it directly, as we're overriding
// the default passport behavior.
req.login(user, function(err) {
if (err) {
failure(err);
}
success();
});
}
}
}
);
};
One idea is to wrap the above code in some more middleware, to make it easier to read:
// This defines what we send back to clients that want to authenticate
// with the system.
var authMiddleware = function(req, res, next) {
var success = function() {
res.send(200, "Login successul");
};
var failure = function(error) {
console.log(error);
res.send(401, "Unauthorized");
};
var middleware = authenticate(req, success, failure);
middleware(req, res, next);
};
// GET /auth/google/return
// Use custom middleware to handle the return from Google.
// The first /auth/google call can remain the same.
app.get('/auth/google/return', authMiddleware);
(This all assumes we're using Express.)