A gem to implement the maker-checker principle. The 4-eyes principle.

Maker-checker (or Maker and Checker, or 4-Eyes) is one of the central principles of authorization in the information systems of financial organizations.The principle of maker and checker means that for each transaction, there must be at least two individuals necessary for its completion. While one individual may create a transaction, the other individual should be involved in confirmation/authorization of the same. Here the segregation of duties plays an important role. In this way, strict control is kept over system software and data, keeping in mind functional division of labor between all classes of employees.

(courtesy Wikipedia)

Working with institutions such as financial institutions you may be required to restrict some actions to be done by two pairs of eyes. FourEyes makes it easy to do this by adding minimal code to the controller with the actions you would like to have verified.

For every action that needs to be authorized, an action containing all the details is stored together with the changes required. The new object or changes are stored on JSON format. This is done after a validation check to ensure that the object will pass validation during the authorization stage. You are responsible for performing the validation check to see if the resource is indeed valid. However, this cannot be guaranteed because the system state may change before authorization to a state that renders the action invalid. In such a scenario, the action would need to be cancelled and created again.

A listing of all pending actions can be availed and depending on any authorization mechanism that you have implemented, a user can then access a pending action and authorize it.

Add this line to your application's Gemfile:

gem 'four_eyes'

And then execute:

$ bundle

Or install it yourself as:

$ gem install four_eyes

Generate the migration files required by running:

rails g four_eyes

To add maker checker functionality, add the following before_filter to the controller in question. Sets up a before filter which adds maker checker functionality to the controller

 class StudentsController < ApplicationController
   add_maker_checker_to_resource
 end

To exempt any one of the actions

 class StudentsController < ApplicationController
   add_maker_checker_to_resource, except: :delete
 end

To include only a subset of the actions

 class StudentsController < ApplicationController
   add_maker_checker_to_resource, only: [:create, :update]
 end

Once that is done, in the create, update or delete action you would call the following

   maker_create([User resource performing the action],
                     [ID of resource performing the action],
                     [Class name of the resource being worked on],
                     [Parameters of oject/resource in JSON format])  

For example, in a system where the users are called Administrators, and the resource we are trying to create via maker checker is a Student, the call to create a student via maker-checker would look like this.

 def create
     maker_create('Administrator',
                   current_administrator_id,
                   'Student',
                   student_params.to_json)    
 end  
                   
 def update
    maker_update('Administrator',
                 current_administrator_id,
                 'Student',
                 student_params.to_json)   
 end
 
 def destroy
    maker_delete('Administrator',
                 'current_administrator_id,
                 'Student',
                 student.to_json)
 end

Minimal vies have been provided for viewing pending and authorized actions. You will probably want to override these and style them accordingly to your application.

Please note four_ayes is agnostic for the type of authorization system you are using. Right now the only check that is performed is ensuring that the maker of an action cannot be the same person to authorize an action. You can extend this to your own authorization system. For example using CanCan you can have something like this for a certain role:

   class AdminAbility
     include CanCan::Ability
     
     def initialize(admin)
       admin ||= Administrator.new
       if admin.role? :Manager
         can :authorize, FourEyes::Action, object_resource_class_name: %w(Student Teacher)
         can :cancel, FourEyes::Action
       end
     end
   end 

1. Fork it ( https://github.com/[my-github-username]/four_eyes/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request