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https://github.com/chaps-io/access-granted

Multi-role and whitelist based authorization gem for Rails (and not only Rails!)
https://github.com/chaps-io/access-granted

access-control authorization cancan permissions rails ruby

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Multi-role and whitelist based authorization gem for Rails (and not only Rails!)

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# AccessGranted [![Code Climate](https://codeclimate.com/github/pokonski/access-granted.png)](https://codeclimate.com/github/pokonski/access-granted)



AccessGranted is a multi-role and whitelist based authorization gem for Rails. And it's lightweight (~300 lines of code)!



## Installation



Add the gem to your gemfile:



```ruby

gem 'access-granted', '~> 1.3'

```

Run the bundle command to install it. Then run the generator:



    rails generate access_granted:policy



### Supported Ruby versions



Because it has **zero** runtime dependencies it is guaranteed to work on all supported MRI Ruby versions, see CI to check the up to date list.

It might and probably is working on Rubinius and JRuby but we are no longer testing against those.



## Summary



AccessGranted is meant as a replacement for CanCan to solve major problems:



1. Performance



    On average AccessGranted is **20 times faster** in resolving identical permissions and takes less memory.

    See [benchmarks](https://github.com/chaps-io/access-granted/blob/master/benchmarks).



2. Roles



    Adds support for roles, so no more `if`s and `else`s in your Policy file. This makes it extremely easy to maintain and    read the code.



3. Whitelists



    This means that you define what the user can do, which results in clean, readable policies regardless of application complexity.

    You don't have to worry about juggling `can`s and `cannot`s in a very convoluted way!



    _Note_: `cannot` is still available, but has a very specifc use. See [Usage](#usage) below.



4. Framework agnostic



    Permissions can work on basically any object and AccessGranted is framework-agnostic,

    but it has Rails support out of the box. :)

    It does not depend on any libraries, pure and clean Ruby code. Guaranteed to always work,

    even when software around changes.



## Usage



Roles are defined using blocks (or by passing custom classes to keep things tidy).



**Order of the roles is VERY important**, because they are being traversed in top-to-bottom order.

At the top you must have an admin or some other important role giving the user top permissions, and as you go down you define less-privileged roles.



**I recommend starting your adventure by reading the [wiki page on how to start with Access Granted](https://github.com/chaps-io/access-granted/wiki/Role-based-authorization-in-Rails), where I demonstrate its abilities on a real life example.**



### Defining an access policy



Let's start with a complete example of what can be achieved:



```ruby

# app/policies/access_policy.rb



class AccessPolicy

  include AccessGranted::Policy



  def configure

    # The most important admin role, gets checked first

    role :admin, { is_admin: true } do

      can :manage, Post

      can :manage, Comment

    end



    # Less privileged moderator role

    role :moderator, proc {|u| u.moderator? } do

      can [:update, :destroy], Post

      can :update, User

    end



    # The basic role. Applies to every user.

    role :member do

      can :create, Post



      can [:update, :destroy], Post do |post, user|

        post.author == user && post.comments.empty?

      end

    end

  end

end

```



#### Defining roles



Each `role` method accepts the name of the role you're creating and an optional matcher.

Matchers are used to check if the user belongs to that role and if the permissions inside should be executed against it.



The simplest role can be defined as follows:



```ruby

role :member do

  can :read, Post

  can :create, Post

end

```



This role will allow everyone (since we didn't supply a matcher) to read and create posts.



But now we want to let admins delete those posts.

In this case we can create a new role above the `:member` to add more permissions for the admin:



```ruby

role :admin, { is_admin: true } do

  can :destroy, Post

end



role :member do

  can :read, Post

  can :create, Post

end

```



The `{ is_admin: true }` hash is compared with the user's attributes to see if the role should be applied to it.

So, if the user has an attribute `is_admin` set to `true`, then the role will be applied to it.



**Note:** you can use more keys in the hash to check many attributes at once.



#### Hash conditions



Hashes can be used as matchers to check if an action is permitted.

For example, we may allow users to only see published posts, like this:



```ruby

role :member do

  can :read, Post, { published: true }

end

```



#### Block conditions



Sometimes you may need to dynamically check for ownership or other conditions,

this can be done using a block condition in `can` method, like so:



```ruby

role :member do

  can :update, Post do |post, user|

    post.author_id == user.id

  end

end

```



When the given block evaluates to `true`, then `user` is allowed to update the post.



#### Roles in order of importance



Additionally, we can allow admins to update **all** posts despite them not being authors like so:



```ruby

role :admin, { is_admin: true } do

  can :update, Post

end



role :member do

  can :update, Post do |post, user|

    post.author_id == user.id

  end

end

```



As stated before: **`:admin` role takes precedence over `:member`** role, so when AccessGranted sees that admin can update all posts, it stops looking at the less important roles.



That way you can keep a tidy and readable policy file which is basically human readable.



### Usage with Rails



AccessGranted comes with a set of helpers available in Ruby on Rails apps:



#### Authorizing controller actions



```ruby

class PostsController

  def show

    @post = Post.find(params[:id])

    authorize! :read, @post

  end



  def create

    authorize! :create, Post

    # (...)

  end

end

```



`authorize!` throws an exception when `current_user` doesn't have a given permission.

You can rescue from it using `rescue_from`:



```ruby

class ApplicationController < ActionController::Base

  rescue_from "AccessGranted::AccessDenied" do |exception|

    redirect_to root_path, alert: "You don't have permission to access this page."

  end

end

```



You can also extract the action and subject which raised the error,

if you want to handle authorization errors differently for some cases:

```ruby

  rescue_from "AccessGranted::AccessDenied" do |exception|

    status = case exception.action

      when :read # invocation like `authorize! :read, @something`

        403

      else

        404

      end



    body = case exception.subject

      when Post # invocation like `authorize! @some_action, Post`

        "failed to access a post"

      else

        "failed to access something else"

      end

  end

```



You can also have a custom exception message while authorizing a request.

This message will be associated with the exception object thrown.



```ruby

class PostsController

  def show

    @post = Post.find(params[:id])

    authorize! :read, @post, 'You do not have access to this post'

    render json: { post: @post }

  rescue AccessGranted::AccessDenied => e

    render json: { error: e.message }, status: :forbidden

  end

end

```



#### Checking permissions in controllers



To check if the user has a permission to perform an action, use the `can?` and `cannot?` methods.



**Example:**



```ruby

class UsersController

  def update

    # (...)



    # only admins can elevate users to moderator status



    if can? :make_moderator, @user

      @user.moderator = params[:user][:moderator]

    end



    # (...)

  end

end

```



#### Checking permissions in views



Usually you don't want to show "Create" buttons for people who can't create something.

You can hide any part of the page from users without permissions like this:



```erb

# app/views/categories/index.html.erb



<% if can? :create, Category %>

  <%= link_to "Create new category", new_category_path %>

<% end %>

```



#### Customizing policy



By default, AccessGranted adds this method to your controllers:



```ruby

  def current_policy

    @current_policy ||= ::AccessPolicy.new(current_user)

  end

```



If you have a different policy class or if your user is not stored in the `current_user` variable, then you can override it in any controller and modify the logic as you please.



You can even have different policies for different controllers!



### Usage with pure Ruby



Initialize the Policy class:



```ruby

policy = AccessPolicy.new(current_user)

```



Check the ability to do something:



with `can?`:



```ruby

policy.can?(:create, Post) #=> true

policy.can?(:update, @post) #=> false

```



or with `cannot?`:



```ruby

policy.cannot?(:create, Post) #=> false

policy.cannot?(:update, @post) #=> true

```



## Common examples



### Extracting roles to separate files



Let's say your app is getting bigger and more complex. This means your policy file is also getting longer.



Below you can see an extracted `:member` role:



```ruby

class AccessPolicy

  include AccessGranted::Policy



  def configure

    role :administrator, is_admin: true do

      can :manage, User

    end



    role :member, MemberRole, -> { |user| !u.guest? }

  end

end



```



And roles should look like this:



```ruby

# app/roles/member_role.rb



class MemberRole < AccessGranted::Role

  def configure

    can :create, Post

    can :destroy, Post do |post, user|

      post.author == user

    end

  end

end

```



## Compatibility with CanCan



This gem has been created as a replacement for CanCan and therefore it requires minimum work to switch.



### Main differences



1. AccessGranted does not extend ActiveRecord in any way, so it does not have the `accessible_by?`

   method which could be used for querying objects available to current user.

   This was very complex and only worked with permissions defined using hash conditions, so

   I decided to not implement this functionality as it was mostly ignored by CanCan users.



2. Both `can?`/`cannot?` and `authorize!` methods work in Rails controllers and views, just like in CanCan.

   The only change you have to make is to replace all `can? :manage, Class` with the exact action to check against.

   `can :manage` is still available for **defining** permissions and serves as a shortcut for defining `:create`, `:read`, `:update`, `:destroy` all in one line.



3. Syntax for defining permissions in the AccessPolicy file (Ability in CanCan) is exactly the same,

   with roles added on top. See [Usage](#usage) above.



## Contributing



1. Fork it

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 new pull request