Trust

Trust is a no-nonsense framework for authorization control - for Ruby On Rails.

  • Why yet another authorization framework you may ask?

Well, we used DeclarativeAuthorization for a while, but got stuck when it comes to name-spaces and inheritance. So, we investigated in the possibilities of using CanCan and CanTango, and found that CanCan could be slow, because all permissions has to be loaded on every request. CanTango has tackled this problem by implementing caching, but the framework is still evolving and seems fairly complex. At the same time, CanTango is role focused and not resource focused.

What will you benefit from when using Trust?

  • Resource focused permissions, not role focused
  • Complete support for inheritance in controllers
  • Complete support for namespaces, both controllers and models
  • Complete support for nested resources
  • Complete support for shortened associations (e.g. if you have models in name spaces that relates to other models in the name space)
  • Fast permission loading, where no cashing is needed. All permissions are declared on class level, so once loaded, they stay in memory.
  • Support for inheritance in the permissions model
  • Natural code evaluation in the permission declarations, i.e. you understand completely what is going on, because the implementation is done the way you implement condifitions in rails for validations and alike.
  • Automatic loading of instances and parents in controller
  • Mongoid support

What is not supported in Trust

  • Loading datasets for the index action. You may use other plugins / gems for doing this, or you may implement your own mechanism.

Install and Setup

Install the gem

gem install trust

Or, in your Gemfile

gem 'trust'

Define permissions

Create the permissions file in your model directory. Example

module Permissions
  class Default < Trust::Permissions
    role :system_admin do
      can :manage
      can :audit
    end
  end

  class Account < Default
    role :support, can(:manage)
    role :accountant do
      can :edit, :show, :if => :associated_with_client?
    end
    role :department_manager, :accountant do
      can :create, :if => lambda { parent }
    end

    def associated_with_client?
      parent && parent.is_a?(Client) && parent.operators.find(user.id)
    end
  end
end

The following attributes will be accessible in a Permissions class:

  • subject - the resource that is currently being tested for authorization
  • parent - the parent of the authorization when resource is nested
  • user - the user accessing the resource
  • klass - the resource class
  • action - the action that triggered the authorization

Keep in mind that the permission object will be instanciated to do authorization, and not the class. You can extend the Trust::Permissions with more functionality if needed.

You can also create aliases for actions. We have defined a predefined set of aliases. See Trust::Permissions.action_aliases. Processing of aliases are done in such way that permissions per action is expanded when the permissions are loaded, so thif you define :update when declaring the permissions, there will be one permission for :update and one for :edit

Apply access control in controller

Place trustee in your controller after the user has been identified. Something like this:

class AccountsController < ApplicationController
  login_required
  trustee
end

The trustee statement will set up 3 before_filters in your controller:

before_filter :set_user
before_filter :load_resource
before_filter :access_control

Trust assumes that current_user is accessible. The user object must respond to the method role_symbols which should return an array of one or more roles for the user.

Handling access denied situations in your controller. Implement something like the following in your ApplicationController:

class ApplicationController < ActionController::Base
  rescue_from Trust::AccessDenied do |exception|
    redirect_to root_url, :alert => exception.message
    # or some other redirect
  end
end

Define associations in your controller

For nested resources you can easily define the associations using belongs_to like this:

class AccountsController < ApplicationController
  login_required
  belongs_to :client
  trustee
end

You can specify as many associations as you like.

The can? and permits? method

The can? method is accessible from controller and views. Here are some coding examples:

In controller or views you will use can?

can? :edit                          # does the current user have permission to edit the current resource? 
                                    # If there is a nested resource, the parent is automatically associated
can? :edit, @customer               # does the current user have permission to edit the given customer? 
                                    # Parent is also passed on here.
can? :edit, @account, @client       # is current user allowed to edit the account associated with the client?

On ActiveRecord objects you will use permits?

@customer.permits? :edit                             # does the current user have permission to edit the given customer?
Customer.permits? :create, @client                   # does the current user have permission to create customers for client?
Customer.permits? :create, @client, :by => @auditor  # does the auditor have permission to create customers?
Customer.permits? :create, :for => @client, :by => @auditor  # same as above

You can also designate actors in your model so you can test if other people has access to do operations on a subject

Include the Actor role in the class

class Auditor
  include Trust::Actor
  ...
end

Now you can test if the auditor has permission to modify customer for client. Three ways of writing it

  @auditor.can? :update, @customer, @client
  @auditor.can? :update, @customer, :for => @client
  @auditor.can? :update, @customer, :parent => @client

The above is the same as

@customer.permits? :update, @client, :by => @auditor 

Instance variables

The filter load_resource will automatically load the instance for the resource in the controller. It will by default use the controller_path to determine the name of the instance variable. Here are a couple of examples:

UsersController => @user
Account::CreditsController => @account_credit

If it is a nested resource, it will also instantiate the parent class, using the namedefined in belongs_to to determine the name. E.g. if you have defined belongs_to :client, it will look for the parameter :client_id and perform a find like Client.find(client_id). Finding the resource will be done through the association between the two, such as client.accounts.find(id).

You can override the naming by specifying model like this

class AccountsController < ApplicationController
  login_required
  model :wackount
  trustee
end

If you want to override the name with namespacing then

class Account::CreditsController < ApplicationController
  login_required
  model :"account/wreckit"
  trustee
end

You can also access the instances in a generic manner if you like. Use following statements:

resource.instance => accesses the instance variable
resource.parent   => accesses the parent instance

You can even assign these if you like. The resource is also exposed as helper, so you can access it in views. For simplicity we have also exposed an instances accessor that you can assign when you have a multirecord result, such as for index action.

Overriding defaults

Overriding resource permits in the controller

Say you have a controller without a model or do not want to perform access control. You can turn off the featur in your controller

class ApplicationController < ActionController::Base
  login_required
  trustee  # By default we want to test for permissions
end

class MyController < ApplicationController
  trustee :off   # turns off all callbacks
end

Alternatives

class MyController < ApplicationController
  set_user :off         # turns off set_user callback
  load_resource :off    # do not load resources
  access_control :off   # turn access control off
end

More specifically

For all call backs and trustee you can use :only and :except options. Example toggle create action off Ruby class MyController < ApplicationController load_resource :except => :create access_control :except => :create end

Yet another alternative, avoiding resource loading

Avoid resource loading on show action Ruby class MyController < ApplicationController actions :except => :show end

Overriding set_user

If you prefer to use some other user reference than current_user you can override the method set_user like this in your controller:

def set_user
  Trust::Authorization.user = User.current
end

Devise integration

If you have your ApplicationController as the trustee you will need to reverse this in devise that inherits the ApplicationController. Add this to your devise initializer:

DeviseController.trustee :off