```ruby
module Devise
  module Models

    # Validatable creates all needed validations for a user email and password.
    # It's optional, given you may want to create the validations by yourself.
    # Automatically validate if the email is present, unique and it's format is
    # valid. Also tests presence of password, confirmation and length
    module Validatable

      # Email regex used to validate email formats. Retrieved from authlogic.
      EMAIL_REGEX = /\A[\w\.%\+\-]+@(?:[A-Z0-9\-]+\.)+(?:[A-Z]{2,4}|museum|travel)\z/i

      def self.included(base)
        base.class_eval do

          validates_presence_of     :email
          validates_uniqueness_of   :email, :allow_blank => true
          validates_format_of       :email, :with => EMAIL_REGEX, :allow_blank => true

          validates_presence_of     :password, :if => :password_required?
          validates_confirmation_of :password, :if => :password_required?
          validates_length_of       :password, :within => 6..20, :allow_blank => true, :if => :password_required?
        end
      end

      protected

        # Checks whether a password is needed or not. For validations only.
        # Passwords are always required if it's a new record, or if the password
        # or confirmation are being set somewhere.
        def password_required?
          new_record? || !password.nil? || !password_confirmation.nil?
        end
    end
  end
end
```

Make validations based on authentication keys.
user
```ruby
module Devise
  module Models

    # Validatable creates all needed validations for a user email and password.
    # It's optional, given you may want to create the validations by yourself.
    # Automatically validate if the email is present, unique and it's format is
    # valid. Also tests presence of password, confirmation and length
    module Validatable

      # Email regex used to validate email formats. Retrieved from authlogic.
      EMAIL_REGEX = /\A[\w\.%\+\-]+@(?:[A-Z0-9\-]+\.)+(?:[A-Z]{2,4}|museum|travel)\z/i

      def self.included(base)
        base.class_eval do
          attribute = authentication_keys.first

          validates_presence_of   attribute
          validates_uniqueness_of attribute, :allow_blank => true
          validates_format_of     attribute, :with => EMAIL_REGEX, :allow_blank => true,
                                              :scope => authentication_keys[1..-1]

          with_options :if => :password_required? do |v|
            v.validates_presence_of     :password
            v.validates_confirmation_of :password
            v.validates_length_of       :password, :within => 6..20, :allow_blank => true
          end
        end
      end

      protected

        # Checks whether a password is needed or not. For validations only.
        # Passwords are always required if it's a new record, or if the password
        # or confirmation are being set somewhere.
        def password_required?
          new_record? || !password.nil? || !password_confirmation.nil?
        end
    end
  end
end
```
assistant