Sevn - an authorization gem for Ruby

Sevn was built based on Six, but +1'd, to make it a little more robust, but not as other gems.

Sevn is still a baby, any help fixing bugs or improving the code is greatly appreciated.

gem install sevn

1. Create your rule pack
2. Create actions check in your rule pack, you can also add aliases, general abilities, and an array of abilities
3. Create abilities object
4. Check abilities for the object

Rules Packs are ruby classes, that inherit from Sevn::RulesPack, they are in charge of telling if an object is allowed to perform and action on a subject, the rule pack should be specific for the subject, usually defined the subject class, but can also be manually defined by the subject.

1. general_abilities

• is an Array of actions (abilities) that any object has access for any subject, in other words, no check is performed, just the presence of the :action in the array.
• This method can be overriden in the Rule Pack

2. abilities(object, subject)

• Method that receives object and subject, and can return an Array of abilities based on the checks you decide to make.
• This method can be overriden in the Rule Pack

3. action_aliases

• Method that returns a Hash of the type { :action => :alias }, the Rule Pack would first try to verify if the :action is allowed, if not, it would then try to see if the :action is aliased via the action_aliases Hash, if so then it would try to verify if the :alias is allowed.
• This method can be overriden in the Rule Pack

1. sevn_#{action}(object, subject)

• Rules pack can define as many sevn_#{action} methods as needed for all the actions needed,it would verify if the object can execute the action for the subject.
• should return a Boolean.

1. Overriding general_abilities

class BookRules < Sevn::RulesPack
  def general_abilities
    [:read, :buy]
  end
end

2. Overriding abilities

class BookRules < Sevn::RulesPack
  def abilities(object, book)
    actions = []
    actions << :write if object.is_writer?
    actions << :sell if object.is_publisher?
    actions << :edit if object.is_writer_of?(book)
    actions
  end
end

3. Overriding action_aliases

class BookRules < Sevn::RulesPack
  def action_aliases
    { :get => :buy, :view => :read }
  end
end

4. Creating action methods:

class BookRules < Sevn::RulesPack
  def sevn_write(object, book)
    object.is_writer?
  end

  def sevn_edit(object, book)
    object.is_writer_of?(book)
  end
end

The abilities object is in charge of choosing the right rule pack for that subject, verifying if the action is allowed, and authorizing the action.

abilites = Sevn::Ability.new({
  :book => Bookrules.new
})

The abilities object is initialized with a Hash, the keys are the identifiers of the rule pack, and the object in the Hash is an object for that rule pack.

There are 2 methods for the abilities object

1. allowed?(object, action, subject, options = {}) - This method will return true or false, based on the abilities defined in the rule pack which was selected for a subject. - If action is an Array, it would return true only if the object can perform all actions. - If the subject is an Array, it would group the subjects by class, and run validations on each of the subjects, it would return true only if all the subjects can perform the action. - The option can be :use_pack => :pack_name, which would force the check to use that specific rule_pack
2. authorize!(object, action, subject, options = {}) - Same behaviour as allowed? but it would raise a Sevn::Errors::UnauthorizedError instead of returning false.

The Abilities object chooses a rule in 1 of these ways

1. if options[:use_pack] is passed, it will choose the pack sent in the options.
2. if the subject is a class subject.kind_of?(Class) then: 1. if the subject defines the method sevn_rule_pack it would use the rule pack returned from calling that method. 2. if none of the above happens, it would underscore the class name and use it as the rule pack, for instance Book becomes :book, BigBook becomes :big_book.
3. if none of the above is true, then: 1. if the subject defines the method sevn_rule_pack it would use the rule pack returned from calling that method. 2. if the subject's class defines the method sevn_rule_pack it would use the rule pack returned from calling that method. 3. if none of the above happens, it would underscore the class of the subject and use it as the rule pack, for instance Book becomes :book, BigBook becomes :big_book.
4. if no rule pack is defined, it will raise a Sevn::Errors::NoPackError

# application_controller.rb
class ApplicationController < ActionController::Base
  protect_from_forgery

  helper_method :current_abilities, :can?, :authorize!

  protected

  def current_abilities
    @current_abilities ||= Sevn::Ability.new({
      :book => BookRules.new
    })
  end

  # simple delegate method for controller & view
  def can?(object, action, subject)
    current_abilities.allowed?(object, action, subject)
  end

  # alternatively, a more CanCan way of using it
  #def can?(action, subject)
  #  current_abilities.allowed?(current_user, action, subject)
  #end

  # simple delegate method for controller & view
  def authorize!(object, action, subject)
    current_abilities.authorize?(object, action, subject)
  end

  # alternatively, a more CanCan way of using it
  #def authorize!(action, subject)
  #  current_abilities.authorize!(current_user, action, subject)
  #end
end

# books_controller.rb
class BooksController < ApplicationController
  before_filter :load_author, except: [:index]
  before_filter :load_publisher, only: [:index]
  before_filter :load_and_authorize_book

  def index
  end

  def show
  end

  def edit
  end

  protected

  def load_author
    @author = Author.find(params[:author_id])
  end

  def load_publisher
    @publisher = Publisher.find(params[:publisher_id])
  end

  def load_and_authorize_book
    action = params[:action].to_sym
    case action
    when :index
      @books = Book.all
      object = @publisher
    when :show
      @book = Book.find(params[:id])
      object = :guest
    when :edit
      @book = Book.find(params[:id])
      object = @author
    end

    authorize!(object, action, @book || @books)
  end
end

The suggested location for rules pack is app/rules/ but they can be anywhere under app/

# app/rules/book_rules.rb
class BookRules < Sevn::RulesPack
  def action_aliases
    {
      edit_book: :edit
    }
  end

  # Note that even when index is an action applied to an array of books,
  # the check is performed on an inividual basis, so consider book as a single book
  def sevn_index(publisher, book)
    publisher.books.include?(book)
  end

  def sevn_show(user, book)
    object == :guest
  end

  def sevn_edit(author, book)
    author.books.include?(book)
  end
end

# Model
class Book < ActiveRecord::Base
  belongs_to :author
  belongs_to :publisher
end

class Author < ActiveRecord::Base
  has_many :books

  def self.sevn_rule_pack
    :user
  end
end

# Schema defined as: Publisher(id: integer, name: string, email: string, sevn_rule_pack: string)
# Note how sevn_rule_pack can be defined per object, and saved to the database
class Publisher < ActiveRecord::Base
  has_many :books
end

link_to 'Edit', edit_book_path(book) if can?(@author, :edit_book, @book)