setuppassport.js

var passport = require("passport");
var User = require("./models/user");
var LocalStrategy = require("passport-local").Strategy;

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." });
    			}
    		});
    	});
    }
));

module.exports = function() {
  	passport.serializeUser(function(user, done) {
        done(null, user._id);
	});
	passport.deserializeUser(function(id, done) {
	    User.findById(id, function(err, user) {
			done(err, user);
		});
	});
};