Critic inserts an easily verifiable authorization layer into your MVC application using resource policies.
Add this line to your application's Gemfile:
gem 'critic'And then execute:
$ bundle
Or install it yourself as:
$ gem install critic
A policy contains authorization logic for a resource and an authenticated subject.
# app/policies/post_policy.rb
class PostPolicy
include Critic::Policy
endThere are two types of methods:
- action - determines if subject is authorized to perform a specific operation on the resource
- scope - returns a list of resources available to the subject
The default scope is index but it can be overridden by specifying .scope.
# app/policies/post_policy.rb
class PostPolicy
include Critic::Policy
# set default scope
self.scope = :author_index
# now default scope
def author_index
resource.where(author_id: subject.id)
end
# no longer the default scope
def index
resource.order(:created_at)
end
endThe most basic actions return true or false to indicate the authorization status.
# app/policies/post_policy.rb
class PostPolicy
include Critic::Policy
def update?
!resource.locked? &&
resource.published_at.present?
end
endThis policy will only allow updates if the post is not locked.
Verify authorization using #authorize.
Post = Struct.new(:locked)
User = Struct.new
PostPolicy.authorize(:update?, User.new, Post.new(false)).granted? #=> true
PostPolicy.authorize(:update?, User.new, Post.new(true)).granted? #=> falseReturning a String from your action is interpreted as a failure. The String is added to the messages of the authorization.
Post = Struct.new(:author_id)
User = Struct.new(:id)
class PostPolicy
include Critic::Policy
def destroy?
return true if resource.author_id == subject.id
"Cannot destroy Post: This post is authored by #{resource.author_id}"
end
end
authorization = PostPolicy.authorize(destroy?, User.new(1), Post.new(2))
authorization.granted? #=> false
authorization.messages #=> ["Cannot destroy Post: This post is authored by 2"']halt can be used to indicate early failure. The argument provided to halt becomes the result of the authorization.
Post = Struct.new(:author_id)
User = Struct.new(:id)
class PostPolicy
include Critic::Policy
def destroy?
if resource.author_id != subject.id
halt "Cannot destroy Post: This post is authored by #{resource.author_id}"
end
true
end
end
authorization = PostPolicy.authorize(destroy?, User.new(1), Post.new(2))
authorization.granted? #=> false
authorization.messages #=> ["Cannot destroy Post: This post is authored by 2"']halt(true) indicates immediate success.
Post = Struct.new(:author_id)
User = Struct.new(:id)
class PostPolicy
include Critic::Policy
def destroy?
check_ownership
false
end
private
def check_ownership
halt(true) if resource.author_id == subject.id
end
end
authorization = PostPolicy.authorize(destroy?, User.new(1), Post.new(2))
authorization.granted? #=> false
authorization.messages #=> ["Cannot destroy Post: This post is authored by 2"']Scopes treat resource as a starting point and return a restricted set of associated resources. Policies can have any number of scopes. The default scope is #index.
# app/policies/post_policy.rb
class PostPolicy
include Critic::Policy
def index
resource.where(deleted_at: nil, author_id: subject.id)
end
endVerify authorization using #authorize.
Post = Class.new(ActiveRecord::Base)
User = Struct.new
authorization = PostPolicy.authorize(index, User.new, Post.new(false))
authorization.granted? #=> true
authorization.result #=> <#ActiveRecord::Relation..>It can be a useful convention to add a ? suffix to your action methods. This allows a clear separation between actions and scopes. All other methods should be protected, similar to Rails controller.
# app/policies/post_policy.rb
class PostPolicy
include Critic::Policy
# default scope
def index
resource.where(published: true)
end
# custom scope
def author_index
resource.where(author_id: subject.id)
end
# action
def show?
(post.draft? && authored_post?) || post.published?
end
protected
alias post resource
def authored_post?
subject == post.author
end
endControllers are the primary consumer of policies. Controllers ask the policy if an authenticated subject is authorized to perform a specific action on a specific resource.
In Rails, the policy action is inferred from params[:action] which corresponds to the controller action method name.
When authorize fails, a Critic::AuthorizationDenied exception is raised with reference to the performed authorization.
# app/controllers/post_controller.rb
class PostController < ApplicationController
include Critic::Controller
rescue_from Critic::AuthorizationDenied do |exception|
messages = exception.authorization.messages || exception.message
render json: {errors: [messages]}, status: :unauthorized
end
def update
post = Post.find(params[:id])
authorize post # calls PostPolicy#update
render json: post
end
endWhen action cannot be inferred, pass the intended action to authorize.
# app/controllers/post_controller.rb
class PostController < Sinatra::Base
include Critic::Controller
error Critic::AuthorizationDenied do |exception|
messages = exception.authorization.messages || exception.message
body {errors: [*messages]}
halt 403
end
put '/posts/:id' do |id|
post = Post.find(id)
authorize post, :update
post.to_json
end
endCalling authorized? returns true or false instead of raising an exception.
# app/controllers/post_controller.rb
class PostController < Sinatra::Base
include Critic::Controller
put '/posts/:id' do |id|
post = Post.find(id)
halt(403) unless authorized?(post, :update)
post.to_json
end
endverify_authorized enforces that the request was authorized before the response is returned. A Critic::AuthorizationMissing error is raised in this case. A request is authorized if authorized?, authorize or authorizing! is called before the response is returned.
# app/controllers/post_controller.rb
class PostController < Sinatra::Base
include Critic::Controller
verify_authorized
error Critic::AuthorizationMissing do |exception|
# notify developers that something has gone horribly wrong
halt 503
end
put '/posts/:id' do |id|
post = Post.find(id)
post.to_json
end
endThis check can be artificially skipped calling authorizing!.
# app/controllers/invitation_controller.rb
class InvitationController < Sinatra::Base
include Critic::Controller
verify_authorized
post '/invitation/accept/code' do |code|
invitation = Invitiation.find_by(code: code)
invitation.accept!
authorizing! # Skip authorization check
redirect '/'
end
endUse authorize_scope and provide the base scope. The return value is the result.
# app/controllers/post_controller.rb
class PostController < Sinatra::Base
include Critic::Controller
get '/customers/:customer_id/posts' do |customer_id|
posts =
authorize_scope(Post.where(customer_id: customer_id))
posts.to_json
end
endCustom indexes can be used by passing an action parameter.
# app/controllers/post_controller.rb
class PostController < Sinatra::Base
include Critic::Controller
get '/posts' d
posts =
authorize_scope(Post, action: :custom_index)
posts.to_json
end
endBy default, the policy's subject is referenced by current_user. Override critic to customize.
# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
include Critic::Controller
protected
def critic
token
end
endThe default policy for a resource is referenced by the resoure class name. For instance, Critic will look for a PostPolicy for a Post.new object. You can set a custom policy for the entire controller by overriding the policy method.
# app/controllers/post_controller.rb
class PostController < ActionController::Base
include Critic::Controller
protected
def policy(_resource)
V2::PostPolicy
end
endYou can also provide a specific policy when calling authorize
# app/controllers/post_controller.rb
class PostController < ActionController::Base
include Critic::Controller
def show
post = Post.find(params[:id])
authorize post, policy: V2::PostPolicy
render json: post
end
endbundle exec rake spec
After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.
Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/critic.