rails--rails/activemodel/lib/active_model/secure_password.rb

require 'bcrypt'

module ActiveModel
  module SecurePassword
    extend ActiveSupport::Concern

    module ClassMethods
      # Adds methods to set and authenticate against a BCrypt password.
      # This mechanism requires you to have a password_digest attribute.
      #
      # Validations for presence of password, confirmation of password (using
      # a "password_confirmation" attribute) are automatically added.
      # You can add more validations by hand if need be.
      #
      # Example using Active Record (which automatically includes ActiveModel::SecurePassword):
      #
      #   # Schema: User(name:string, password_digest:string)
      #   class User < ActiveRecord::Base
      #     has_secure_password
      #   end
      #
      #   user = User.new(:name => "david", :password => "", :password_confirmation => "nomatch")
      #   user.save                                                      # => false, password required
      #   user.password = "mUc3m00RsqyRe"
      #   user.save                                                      # => false, confirmation doesn't match
      #   user.password_confirmation = "mUc3m00RsqyRe"
      #   user.save                                                      # => true
      #   user.authenticate("notright")                                  # => false
      #   user.authenticate("mUc3m00RsqyRe")                             # => user
      #   User.find_by_name("david").try(:authenticate, "notright")      # => nil
      #   User.find_by_name("david").try(:authenticate, "mUc3m00RsqyRe") # => user
      def has_secure_password
        attr_reader   :password
        attr_accessor :password_confirmation

        validates_confirmation_of :password
        validates_presence_of     :password_digest
        
        include InstanceMethodsOnActivation

        if respond_to?(:attributes_protected_by_default)
          def self.attributes_protected_by_default
            super + ['password_digest']
          end
        end
      end
    end

    module InstanceMethodsOnActivation
      # Returns self if the password is correct, otherwise false.
      def authenticate(unencrypted_password)
        if BCrypt::Password.new(password_digest) == unencrypted_password
          self
        else
          false
        end
      end

      # Encrypts the password into the password_digest attribute.
      def password=(unencrypted_password)
        @password = unencrypted_password
        self.password_digest = BCrypt::Password.create(unencrypted_password)
      end
    end
  end
end