authlogic_model.rb

module AuthlogicModel
  def self.included(model)
    model.class_eval do
      extend ClassMethods
      include InstanceMethods
      include ProtectedAttributes

      field :username
      field :email
      field :crypted_password
      field :password_salt
      field :persistence_token
      field :login_count, :type => Integer, :default => 0
      field :last_request_at, :type => DateTime
      field :last_login_at, :type => DateTime
      field :current_login_at, :type => DateTime
      field :last_login_ip
      field :current_login_ip

      index :username
      index :email
      index :persistence_token
      index :last_login_at

      include Authlogic::ActsAsAuthentic::Base
      include Authlogic::ActsAsAuthentic::Email
      include Authlogic::ActsAsAuthentic::LoggedInStatus
      include Authlogic::ActsAsAuthentic::Login
      include Authlogic::ActsAsAuthentic::MagicColumns
      include Authlogic::ActsAsAuthentic::Password
      include Authlogic::ActsAsAuthentic::PerishableToken
      include Authlogic::ActsAsAuthentic::PersistenceToken
      include Authlogic::ActsAsAuthentic::RestfulAuthentication
      include Authlogic::ActsAsAuthentic::SessionMaintenance
      include Authlogic::ActsAsAuthentic::SingleAccessToken
      include Authlogic::ActsAsAuthentic::ValidationsScope
    end
  end

  module ClassMethods
    def <(klass)
      return true if klass == ::ActiveRecord::Base
      super(klass)
    end

    def column_names
      fields.map &:first
    end

    def quoted_table_name
      'users'
    end

    def primary_key
      # FIXME: Is this check good enough?
      if caller.first.to_s[/(persist|session)/]
        :"_id"
      else
        super
      end
    end

    def default_timezone
      :utc
    end

    def find_by__id(*args)
      find *args
    end

    # Change this to your preferred login field
    def find_by_username(username)
      where(:username => username).first
    end

    def with_scope(query)
      query = where(query) if query.is_a?(Hash)
      yield query
    end
  end

  module InstanceMethods
    def readonly?
      false
    end
  end
end

protected_attributes.rb

module ProtectedAttributes
  def self.included(base)
    base.class_eval do
      include InstanceMethods
      extend ClassMethods
    end
  end

  module ClassMethods
    def attr_protected(*attributes)
      @@protected_attributes = attributes.collect(&:to_s)
    end

    def protected_attributes
      @@protected_attributes ||= []
    end
  end

  module InstanceMethods
    def write_attributes(attrs = nil)
      attrs = attrs.reject {|k,v| self.class.protected_attributes.include?(k.to_s)}
      process(attrs || {})
      identify if id.blank?
      notify
    end
  end
end

user.rb

class User
  include Mongoid::Document
  include Mongoid::Timestamps

  include AuthlogicModel

  acts_as_authentic do |config|
    # Change this to your preferred login field
    config.login_field = 'username'
    config.instance_eval do
      validates_uniqueness_of_login_field_options :scope => '_id', :case_sensitive => true
    end
  end
end

user_session.rb

class UserSession < Authlogic::Session::Base
  def to_key
    new_record? ? nil : [self.send(self.class.primary_key)]
  end
end