routes.rb
--------------
ActionController::Routing::Routes.draw do |map|
  map.resources :pages
  map.resources :users
  map.index '/', :controller => 'pages',
               :action => 'show',
               :id => '1-welcome-page'
  map.show_user '/user/:username',
               :controller => 'users',
               :action => 'show_by_username'
  map.resources :users, :member => { :enable => :put }
<...>

Model file > user.rb
----------------------
require 'digest/sha2'
class User < ActiveRecord::Base
<...>
 def self.authenticate(username, password)
    find_by_username_and_hashed_password_and_enabled(username,
        User.encrypt(password), true)
  end


app/controllers/account_controler.rb
-----------------------------
class AccountController < ApplicationController
  def authenticate
    self.logged_in_user = User.authenticate(params[:user][:username],
        params[:user][:password])
      if is_logged_in?
      redirect_to index_url
    else
      flash[:error] = "I'm sorry; either your username or password was incorrect."
      redirect_to :action => 'login'
    end
  end