LocalStrategy of passportjs is not being called - node.js

Question

I'm trying to build a login system using passportJS. For some reason, LocalStrategy is not being called from passport.authenticate(). No idea why. Database is mongodb. I have a collection for users in db. Can anyone help me regarding this issue? Thanks. Here is the code:
app.js
var express = require('express');
var bodyParser = require("body-parser");
var mysql = require('mysql');
var path = require('path');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var expressValidator = require('express-validator');
var flash = require('connect-flash');
var session = require('express-session');
var passport = require('passport');
var LocalStrategy = require('passport-local').Strategy;
var mongo = require('mongodb');
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/WelcomeLimoUsa');
var db = mongoose.connection;
var routes = require('./routes/index');
var users = require('./routes/users');
// Init App
var app = express();
// BodyParser Middleware
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
// Set Static Folder
app.use(express.static(__dirname + '/'));
// Express Session
app.use(session({
secret: 'secret',
saveUninitialized: true,
resave: true
}));
// Passport init
app.use(passport.initialize());
app.use(passport.session());
// Express Validator
app.use(expressValidator({
errorFormatter: function(param, msg, value) {
var namespace = param.split('.')
, root = namespace.shift()
, formParam = root;
while(namespace.length) {
formParam += '[' + namespace.shift() + ']';
}
return {
param : formParam,
msg : msg,
value : value
};
}
}));
// Connect Flash
app.use(flash());
// Global Variables
app.use(function (req, res, next) {
res.locals.success_msg = req.flash('success_msg');
res.locals.error_msg = req.flash('error_msg');
res.locals.error = req.flash('error');
res.locals.user = req.user || null;
next();
});
app.use('/admin', routes);
app.use('/users', users);
login.html
<form action="/users/admin" method="post" class="well form-horizontal">
<p>
<strong>Admin User Name: </strong>
<input type="text" name="username" size="25" class="form-control" placeholder="User Name">
<p>
<p>
<strong align="center">Admin Password: </strong>
<input align="center" type="password" size="15" name="password" class="form-control" placeholder="password">
<p>
<p>
<input align="center" type="submit" value="Log In" class="btn btn-success" style="font-weight:600">
<input align="center" type="reset" value="Clear" class="btn btn-default" style="font-weight:600">
</form>
users.js
var express = require('express');
var passport = require('passport');
var LocalStrategy = require('passport-local').Strategy;
var User = require('../models/user');
var router = express.Router();
// Login
router.get('/admin', function(req, res){
res.render('./login.html');
});
router.get('/error', function(req, res){
res.sendfile("./loginerror.html");
});
passport.use(new LocalStrategy(
function(username, password, done) {
User.getUserByUsername(username, function(err, user){
if(err) throw err;
if(!user){
return done(null, false, {message: 'Unknown User'});
}
User.comparePassword(password, user.password, function(err, isMatch){
if(err) throw err;
if(isMatch){
return done(null, user);
} else {
return done(null, false, {message: 'Invalid password'});
}
});
});
}));
passport.serializeUser(function(user, done) {
done(null, user.id);
});
passport.deserializeUser(function(id, done) {
User.getUserById(id, function(err, user) {
done(err, user);
});
});
router.post('/admin', passport.authenticate('local', { successRedirect: '/admin',
failureRedirect: '/users/error',
failureFlash: true }), function(req,res){
var user_name = req.body.userid;
var password=req.body.password;
console.log("User name = " + user_name + ", password is "+ password);
res.redirect('/admin');
});
module.exports = router;
user.js
var mongoose = require('mongoose');
var bcrypt = require('bcryptjs');
// User Schema
var UserSchema = mongoose.Schema({
username: {
type: String,
index:true
},
password: {
type: String
}
});
var User = module.exports = mongoose.model('User', UserSchema);
module.exports.getUserByUsername = function(username, callback){
var query = {username: username};
User.findOne(query, callback);
}
module.exports.getUserById = function(id, callback){
User.findById(id, callback);
}
module.exports.comparePassword = function(candidatePassword, hash, callback){
bcrypt.compare(candidatePassword, hash, function(err, isMatch) {
if(err) throw err;
callback(null, isMatch);
});
}