Passport's serializeUser doesn't respond - node.js

Question

I can't quite figure out how to use Passport's serializeUser function in express/SQL.
Here are my questions:
How does passport.serializeUser know what "user" is? Where should I have specified it?
How does passport.serializeUser know which request object should be bound with a cookie?
My app configuration looks like this:
var passport = require('passport');
app.use(session({ secret: 'Secret',
saveUninitialized: true,
resave: true}));
app.use(passport.initialize());
app.use(passport.session());
I also expose the following code to the app in twitter_auth.js:
// twitter authentication and login
app.get('/auth/twitter', passport.authenticate('twitter'));
// handle callback after twitter has authenticated user
app.get('/auth/twitter/callback',passport.authenticate('twitter',{
successRedirect: '/',
failureRedirect: '/'
}));
// used to serialize user
passport.serializeUser(function(user,done){
done(null,user);
});
// used to deserialize the user
passport.deserializeUser(function(User_ID,done){
connection.query('SELECT * from UsersTable where User_ID = '+User_ID, function(err,rows){
done(err,rows[0]);
});
});
When I try spotting it:
// used to serialize user
passport.serializeUser(function(user,done){
console.log('spotted here!');
done(null,user);
});
I never see anything. What's wrong?

Answer 1

To answer your two questions:
You have to define what 'user' is inside the authentication code.
It should look like this:
passport.use(new TwitterStrategy({
consumerKey:*******,
consumerSecret:******,
callbackURL:'/auth/twitter/callback'
},
function(token, tokenSecret, profile,done){
var user = db.call(retrieve a user) ; //whatever you want it to be
done(null,user);
});
The authentication route was accessed via some request object to begin with, and it's the code there:
done(null,user);
that knows of your req object. From my understanding, that is.
A good source on this is: http://toon.io/understanding-passportjs-authentication-flow/