Node passport flow with Express - node.js

Question

I' learning Node.s and Express, and I'm following this example from https://github.com/EvanHahn/Express.js-in-Action-code/tree/master/Chapter_08/learn-about-me. Can you explain the following question?
In the "/login" post route, if I need to access the request and response objects, how should I do it?
What is the "done" function inside LocalStrategy(), and how I know what parameter to pass? Looks like it take 3 arguments, and the 2nd argument is the user object, and the 3rd argument is the message. What is the 1st argument?
How do the username and password get passed from the "/login" post route into LocalStrategy? What magic is behind the scene?
router.post("/login", passport.authenticate("login", {
successRedirect: "/",
failureRedirect: "/login",
failureFlash: true
}));
passport.use("login", new LocalStrategy(function(username, password, done) {
User.findOne({ username: username }, function(err, user) {
if (err) { return done(err); }
if (!user) {
return done(null, false, { message: "No user has that username!" });
}
user.checkPassword(password, function(err, isMatch) {
if (err) { return done(err); }
if (isMatch) {
return done(null, user);
} else {
return done(null, false, { message: "Invalid password." });
}
});
});
}));

Answer 1

The answer for question #1 and #2 is at http://passportjs.org/docs
app.get('/login', function(req, res, next) {
passport.authenticate('local', function(err, user, info) {
if (err) { return next(err); }
if (!user) { return res.redirect('/login'); }
req.logIn(user, function(err) {
if (err) { return next(err); }
return res.redirect('/users/' + user.username);
});
})(req, res, next);
});
3 is at the same docs page.
passport.use(new LocalStrategy({
usernameField: 'email',
passwordField: 'passwd'
},
function(username, password, done) {
// ...
}
));