Rails' Authentication example

rails__authentication_example.rb

# module
require 'digest/sha2'

module Extensions
  module Authentication
    extend ActiveSupport::Concern

    module ClassMethods
      def find_and_authenticate(attributes)
        @user.authenticate(attributes[:password]) if @user = find_by_email(attributes[:email])
      end
    end

    def encrypt_password(password, salt)
      Digest::SHA2.hexdigest(password << salt)
    end

    def authenticate(password)
      id if hashed_password == encrypt_password(password, salt)
    end

    def password=(password)
      assign_attributes salt: get_or_generate_salt, hashed_password: encrypt_password(password, get_or_generate_salt)
    end

    def get_or_generate_salt
      @salt ||= rand.to_s
    end
  end
end

# model
class User < ActiveRecord::Base
  include Extensions::Authentication
end

# controller
class SessionsController < ApplicationController
  def create
    if session[:user_id] = User.find_and_authenticate(params[:user])
      flash[:notice] = 'User has been logged in'
      redirect_to users_path
    else
      flash.now[:notice] = 'User has not been logged in'
      render new_session_path
    end
  end
end