Taking a domain out of rails example.

account.rb

# The Database model, it does
# validation that is required for db integrity.
class User < ActiveRecord::Base
  validates :presence => :email
end

# Just your average active model, this one handles a login.
# This assumes a railtie that provides a Validator class which takes domain
# as an argument and passes the Login class with its associations to
# the domain class.
class Login < ActiveModel::Base
  belongs_to  :user
  has_one     :session
  has_many    :hours
  validates   :domain => :authentication
  
  delegate    :session_hash, :to => :session
  
end

# In the domain gem
class Authentication < Entity::Base
  validate :password_matches
  validate :account_active
  
  # Actual functions that take the login object and 
  # peruse its information. The Login object is responsible
  # for telling this object how to get its data.
end