generate_and_authenticate_password.rb

require 'active_record'
require 'bcrypt'

class User < ActiveRecord::Base
  PASSWORD_SALT = '$2a$20$ESQ40HbYj00QFse2rbArOe'.freeze
  PASSWORD_COST = 15.freeze

  establish_connection adapter: 'sqlite3', database: ':memory:'
  connection.create_table table_name, force: true do |t|
    t.string :email
    t.string :password
  end

  validates :email, uniqueness: true
  validates :email, :password, presence: true
  before_create :validate_password

  attr_accessor :password_confirmation

  def password=(password)
    @original_password = password
    super ::BCrypt::Password.create(password + PASSWORD_SALT, cost: PASSWORD_COST)
  end

  def password_confirmation=(password)
    @password_confirmation = password
  end

  private
  def validate_password
    if @original_password.to_s == @password_confirmation.to_s
      true
    else
      raise 'Password mismatch'
    end
  end

  def self.authenticate params
    user = User.find_by_email params[:email]
    return false unless user.present?

    password = ::BCrypt::Password.new user.password
    return password == (params[:password] + PASSWORD_SALT) if password.present?

    false
  end
end

# Now we create an user
User.create email: '[email protected]', password: 'pass', password_confirmation: 'pass'

# And assume this is a form data submitted by user
login_params = { email: '[email protected]', password: 'pass'}
puts User.authenticate login_params #=> true

login_params = { email: '[email protected]', password: 'word'}
puts User.authenticate login_params #=> false