Simple and lightweight authorization library for Rails inspired by Pundit.
Banken provides a set of helpers which restricts what resources
a given user is allowed to access.

In first, Look this tutorial:

• Tutorial
• Tutorial (Japanese)

========

What’s the difference between Banken and Pundit?

• The difference between Banken and Pundit
• The difference between Banken and Pundit (Japanese)

Installation

gem "banken"

Include Banken in your application controller:

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  include Banken
  protect_from_forgery
end

Optionally, you can run the generator, which will set up an application loyalty
with some useful defaults for you:

rails g banken:install

After generating your application loyalty, restart the Rails server so that Rails
can pick up any classes in the new app/loyalties/ directory.

Loyalties

Banken is focused around the notion of loyalty classes. We suggest that you put
these classes in app/loyalties. This is a simple example that allows updating
a post if the user is an admin, or if the post is unpublished:

# app/loyalties/posts_loyalty.rb
class PostsLoyalty
  attr_reader :user, :post

  def initialize(user, post)
    @user = user
    @post = post
  end

  def update?
    user.admin? || post.unpublished?
  end
end

As you can see, this is just a plain Ruby class. Banken makes the following
assumptions about this class:

• The class has the same name as some kind of controller class, only suffixed
  with the word “Loyalty”.
• The first argument is a user. In your controller, Banken will call the
  current_user method to retrieve what to send into this argument
• The second argument is optional, whose authorization you want to check.
  This does not need to be an ActiveRecord or even an ActiveModel object,
  it can be anything really.
• The class implements some kind of query method, in this case update?.
  Usually, this will map to the name of a particular controller action.

That’s it really.

Usually you’ll want to inherit from the application loyalty created by the
generator, or set up your own base class to inherit from:

# app/loyalties/posts_loyalty.rb
class PostsLoyalty < ApplicationLoyalty
  def update?
    user.admin? || record.unpublished?
  end
end

In the generated ApplicationLoyalty, the optional object is called record.

Supposing that you are in PostsController, Banken now lets you do
this in your controller:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def update
    @post = Post.find(params[:id])
    authorize! @post
    if @post.update(post_params)
      redirect_to @post
    else
      render :edit
    end
  end
end

The authorize method automatically infers from controller name that Posts will have a matching
PostsLoyalty class, and instantiates this class, handing in the current user
and the given optional object. It then infers from the action name, that it should call
update? on this instance of the loyalty. In this case, you can imagine that
authorize! would have done something like this:

raise "not authorized" unless PostsLoyalty.new(current_user, @post).update?

If you don’t have an optional object for the first argument to authorize!, then you can pass
the class. For example:

Loyalty:

# app/loyalties/posts_loyalty.rb
class PostsLoyalty < ApplicationLoyalty
  def admin_list?
    user.admin?
  end
end

Controller:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def admin_list
    authorize!
    # Rest of controller action
  end
end

You can easily get a hold of an instance of the loyalty through the loyalty
method in both the view and controller. This is especially useful for
conditionally showing links or buttons in the view:

<% if loyalty(@post, :posts).update? %>
  <%= link_to "Edit post", edit_post_path(@post) %>
<% end %>

If you are using namespace in your controller and policy,
you can access the policy passing string like ‘admin/posts’ as a second argument.
Below calls Admin::PostsLoyalty.

<% if loyalty(@post, 'admin/posts').update? %>
  <%= link_to "Edit post", edit_post_path(@post) %>
<% end %>

Ensuring loyalties are used

Banken adds a method called verify_authorized to your controllers. This
method will raise an exception if authorize! has not yet been called. You
should run this method in an after_action to ensure that you haven’t
forgotten to authorize the action. For example:

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  after_action :verify_authorized, except: :index
end

If you’re using verify_authorized in your controllers but need to
conditionally bypass verification, you can use skip_authorization.
These are useful in circumstances where you don’t want to disable verification for the
entire action, but have some cases where you intend to not authorize.

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def show
    record = Record.find_by(attribute: "value")
    if record.present?
      authorize! record
    else
      skip_authorization
    end
  end
end

If you need to perform some more sophisticated logic or you want to raise a custom
exception you can use the two lower level method banken_authorization_performed? which
return true or false depending on whether authorize! have been called, respectively.

Just plain old Ruby

As you can see, Banken doesn’t do anything you couldn’t have easily done
yourself. It’s a very small library, it just provides a few neat helpers.
Together these give you the power of building a well structured, fully working
authorization system without using any special DSLs or funky syntax or
anything.

Remember that all of the loyalty is just plain Ruby classes,
which means you can use the same mechanisms you always use to DRY things up.
Encapsulate a set of permissions into a module and include them in multiple
loyalties. Use alias_method to make some permissions behave the same as
others. Inherit from a base set of permissions. Use metaprogramming if you
really have to.

Generator

Use the supplied generator to generate loyalties:

rails g banken:loyalty posts

Closed systems

In many applications, only logged in users are really able to do anything. If
you’re building such a system, it can be kind of cumbersome to check that the
user in a loyalty isn’t nil for every single permission.

We suggest that you define a filter that redirects unauthenticated users to the
login page. As a secondary defence, if you’ve defined an ApplicationLoyalty, it
might be a good idea to raise an exception if somehow an unauthenticated user
got through. This way you can fail more gracefully.

# app/loyalties/application_loyalty.rb
class ApplicationLoyalty
  def initialize(user, record)
    raise Banken::NotAuthorizedError, "must be logged in" unless user
    @user = user
    @record = record
  end
end

Rescuing a denied Authorization in Rails

Banken raises a Banken::NotAuthorizedError you can
rescue_from
in your ApplicationController. You can customize the user_not_authorized
method in every controller.

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  protect_from_forgery
  include Banken

  rescue_from Banken::NotAuthorizedError, with: :user_not_authorized

  private

  def user_not_authorized
    flash[:alert] = "You are not authorized to perform this action."
    redirect_to(request.referrer || root_path)
  end
end

Creating custom error messages

NotAuthorizedErrors provide information on what query (e.g. :create?), what
controller (e.g. PostsController), and what loyalty (e.g. an instance of
PostsLoyalty) caused the error to be raised.

One way to use these query, record, and loyalty properties is to connect
them with I18n to generate error messages. Here’s how you might go about doing
that.

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  rescue_from Banken::NotAuthorizedError, with: :user_not_authorized

  private

  def user_not_authorized(exception)
    loyalty_name = exception.loyalty.class.to_s.underscore

    flash[:error] = t "#{loyalty_name}.#{exception.query}", scope: "banken", default: :default
    redirect_to(request.referrer || root_path)
  end
end

en:
  banken:
    default: 'You cannot perform this action.'
    posts_loyalty:
      update?: 'You cannot edit this post!'
      create?: 'You cannot create posts!'

Of course, this is just an example. Banken is agnostic as to how you implement
your error messaging.

Customize Banken user

In some cases your controller might not have access to current_user, or your
current_user is not the method that should be invoked by Banken. Simply
define a method in your controller called banken_user.

def banken_user
  User.find_by_other_means
end

Additional context

Banken strongly encourages you to model your application in such a way that the
only context you need for authorization is a user object and a domain model that
you want to check authorization for. If you find yourself needing more context than
that, consider whether you are authorizing the right domain model, maybe another
domain model (or a wrapper around multiple domain models) can provide the context
you need.

Banken does not allow you to pass additional arguments to loyalties for precisely
this reason.

However, in very rare cases, you might need to authorize based on more context than just
the currently authenticated user. Suppose for example that authorization is dependent
on IP address in addition to the authenticated user. In that case, one option is to
create a special class which wraps up both user and IP and passes it to the loyalty.

class UserContext
  attr_reader :user, :ip

  def initialize(user, ip)
    @user = user
    @ip = ip
  end
end

# app/controllers/application_controller.rb
class ApplicationController
  include Banken

  def banken_user
    UserContext.new(current_user, request.ip)
  end
end

Strong parameters

In Rails 4 (or Rails 3.2 with the
strong_parameters gem),
mass-assignment protection is handled in the controller. With Banken you can
control which attributes a user has access to update via your loyalties. You can
set up a permitted_attributes method in your loyalty like this:

# app/loyalties/posts_loyalty.rb
class PostsLoyalty < ApplicationLoyalty
  def permitted_attributes
    if user.admin? || user.owner_of?(post)
      [:title, :body, :tag_list]
    else
      [:tag_list]
    end
  end
end

You can now retrieve these attributes from the loyalty:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def update
    @post = Post.find(params[:id])
    if @post.update_attributes(post_params)
      redirect_to @post
    else
      render :edit
    end
  end

  private

  def post_params
    params.require(:post).permit(loyalty(@post).permitted_attributes)
  end
end

However, this is a bit cumbersome, so Banken provides a convenient helper method:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def update
    @post = Post.find(params[:id])
    if @post.update_attributes(permitted_attributes(@post))
      redirect_to @post
    else
      render :edit
    end
  end
end

License

Licensed under the MIT license, see the separate LICENSE.txt file.