= CanCan

Wiki[https://github.com/ryanb/cancan/wiki] | RDocs[http://rdoc.info/projects/ryanb/cancan] | Screencast[http://railscasts.com/episodes/192-authorization-with-cancan]

CanCan is an authorization library for Ruby on Rails which restricts what resources a given user is allowed to access. All permissions are defined in a single location (the +Ability+ class) and not duplicated across controllers, views, and database queries.


== Installation

In <b>Rails 3</b>, add this to your Gemfile and run the +bundle+ command.

  gem "cancan"

In <b>Rails 2</b>, add this to your environment.rb file.

  config.gem "cancan"

Alternatively, you can install it as a plugin.

  rails plugin install git://github.com/ryanb/cancan.git


== Getting Started

CanCan expects a +current_user+ method to exist in the controller. First, set up some authentication (such as Authlogic[https://github.com/binarylogic/authlogic] or Devise[https://github.com/plataformatec/devise]). See {Changing Defaults}[https://github.com/ryanb/cancan/wiki/changing-defaults] if you need different behavior.


=== 1. Define Abilities

User permissions are defined in an +Ability+ class. CanCan 1.5 includes a Rails 3 generator for creating this class.

  rails g cancan:ability

See {Defining Abilities}[https://github.com/ryanb/cancan/wiki/defining-abilities] for details.


=== 2. Check Abilities & Authorization

The current user's permissions can then be checked using the <tt>can?</tt> and <tt>cannot?</tt> methods in the view and controller.

  <% if can? :update, @article %>
    <%= link_to "Edit", edit_article_path(@article) %>
  <% end %>

See {Checking Abilities}[https://github.com/ryanb/cancan/wiki/checking-abilities] for more information

The <tt>authorize!</tt> method in the controller will raise an exception if the user is not able to perform the given action.

  def show
    @article = Article.find(params[:id])
    authorize! :read, @article
  end

Setting this for every action can be tedious, therefore the +load_and_authorize_resource+ method is provided to automatically authorize all actions in a RESTful style resource controller. It will use a before filter to load the resource into an instance variable and authorize it for every action.

  class ArticlesController < ApplicationController
    load_and_authorize_resource

    def show
      # @article is already loaded and authorized
    end
  end

See {Authorizing Controller Actions}[https://github.com/ryanb/cancan/wiki/authorizing-controller-actions] for more information.


=== 3. Handle Unauthorized Access

If the user authorization fails, a <tt>CanCan::AccessDenied</tt> exception will be raised. You can catch this and modify its behavior in the +ApplicationController+.

  class ApplicationController < ActionController::Base
    rescue_from CanCan::AccessDenied do |exception|
      redirect_to root_url, :alert => exception.message
    end
  end

See {Exception Handling}[https://github.com/ryanb/cancan/wiki/exception-handling] for more information.


=== 4. Lock It Down

If you want to ensure authorization happens on every action in your application, add +check_authorization+ to your ApplicationController.

  class ApplicationController < ActionController::Base
    check_authorization
  end

This will raise an exception if authorization is not performed in an action. If you want to skip this add +skip_authorization_check+ to a controller subclass. See {Ensure Authorization}[https://github.com/ryanb/cancan/wiki/Ensure-Authorization] for more information.


== Wiki Docs

* {Upgrading to 1.5}[https://github.com/ryanb/cancan/wiki/Upgrading-to-1.5]
* {Defining Abilities}[https://github.com/ryanb/cancan/wiki/Defining-Abilities]
* {Checking Abilities}[https://github.com/ryanb/cancan/wiki/Checking-Abilities]
* {Authorizing Controller Actions}[https://github.com/ryanb/cancan/wiki/Authorizing-Controller-Actions]
* {Exception Handling}[https://github.com/ryanb/cancan/wiki/Exception-Handling]
* {Changing Defaults}[https://github.com/ryanb/cancan/wiki/Changing-Defaults]
* {See more}[https://github.com/ryanb/cancan/wiki]


== Questions or Problems?

If you have any issues with CanCan which you cannot find the solution to in the documentation[https://github.com/ryanb/cancan/wiki], please add an {issue on GitHub}[https://github.com/ryanb/cancan/issues] or fork the project and send a pull request.

To get the specs running you should call +bundle+ and then +rake+. See the {spec/README}[https://github.com/ryanb/cancan/blob/master/spec/README.rdoc] for more information.


== Special Thanks

CanCan was inspired by declarative_authorization[https://github.com/stffn/declarative_authorization/] and aegis[https://github.com/makandra/aegis]. Also many thanks to the CanCan contributors[https://github.com/ryanb/cancan/contributors]. See the CHANGELOG[https://github.com/ryanb/cancan/blob/master/CHANGELOG.rdoc] for the full list.