session_store.rb

SSOServer::Application.config.session_store :active_record_store
ActiveRecord::SessionStore.session_class = UserSessionStore

user_session_store_spec.rb

require 'spec_helper'

describe UserSessionStore do
  subject(:store) { UserSessionStore.new(session_id: '123') }

  before do
    store.data[:test] = 'test_data'
    store.data[:sso_session_id] = '3'
    store.save!
    store.reload
  end

  it 'merges sso_session_id into #data' do
    store.data[:sso_session_id].should eq '3'
  end

  it 'saves sso_session_id in separate column' do
    store.sso_session_id.should eq '3'
  end

  it 'doesnt store sso_session_id in marshaled data column' do
    marshaled_data = UserSessionStore.unmarshal(store.read_attribute(:data))
    marshaled_data.count.should eq 1
    marshaled_data.should have_key(:test)
  end
end

user_sessions_store.rb

class UserSessionStore < ActiveRecord::SessionStore::Session
  def self.find_by_session_id(*args)
    super
  end

  def data
    @data ||= super.merge(:sso_session_id => sso_session_id)
  end

  private

  def marshal_data!
    return false unless loaded?
    self.sso_session_id = data[:sso_session_id] if data[:sso_session_id].present?
    write_attribute(@@data_column_name, self.class.marshal(data.except(:sso_session_id)))
  end
end