](https://www.varvet.com)
## Installation
``` ruby
gem "pundit"
```
Include Pundit in your application controller:
``` ruby
class ApplicationController < ActionController::Base
include Pundit
protect_from_forgery
end
```
Optionally, you can run the generator, which will set up an application policy
with some useful defaults for you:
``` sh
rails g pundit:install
```
After generating your application policy, restart the Rails server so that Rails
can pick up any classes in the new `app/policies/` directory.
## Policies
Pundit is focused around the notion of policy classes. We suggest that you put
these classes in `app/policies`. This is a simple example that allows updating
a post if the user is an admin, or if the post is unpublished:
``` ruby
class PostPolicy
attr_reader :user, :post
def initialize(user, post)
@user = user
@post = post
end
def update?
user.admin? or not post.published?
end
end
```
As you can see, this is just a plain Ruby class. Pundit makes the following
assumptions about this class:
- The class has the same name as some kind of model class, only suffixed
with the word "Policy".
- The first argument is a user. In your controller, Pundit will call the
`current_user` method to retrieve what to send into this argument
- The second argument is some kind of model object, 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 policy created by the
generator, or set up your own base class to inherit from:
``` ruby
class PostPolicy < ApplicationPolicy
def update?
user.admin? or not record.published?
end
end
```
In the generated `ApplicationPolicy`, the model object is called `record`.
Supposing that you have an instance of class `Post`, Pundit now lets you do
this in your controller:
``` ruby
def update
@post = Post.find(params[:id])
authorize @post
if @post.update(post_params)
redirect_to @post
else
render :edit
end
end
```
The authorize method automatically infers that `Post` will have a matching
`PostPolicy` class, and instantiates this class, handing in the current user
and the given record. It then infers from the action name, that it should call
`update?` on this instance of the policy. In this case, you can imagine that
`authorize` would have done something like this:
``` ruby
unless PostPolicy.new(current_user, @post).update?
raise Pundit::NotAuthorizedError, "not allowed to update? this #{@post.inspect}"
end
```
You can pass a second argument to `authorize` if the name of the permission you
want to check doesn't match the action name. For example:
``` ruby
def publish
@post = Post.find(params[:id])
authorize @post, :update?
@post.publish!
redirect_to @post
end
```
You can pass an argument to override the policy class if necessary. For example:
```ruby
def create
@publication = find_publication # assume this method returns any model that behaves like a publication
# @publication.class => Post
authorize @publication, policy_class: PublicationPolicy
@publication.publish!
redirect_to @publication
end
```
If you don't have an instance for the first argument to `authorize`, then you can pass
the class. For example:
Policy:
```ruby
class PostPolicy < ApplicationPolicy
def admin_list?
user.admin?
end
end
```
Controller:
```ruby
def admin_list
authorize Post # we don't have a particular post to authorize
# Rest of controller action
end
```
`authorize` returns the object passed to it, so you can chain it like this:
Controller:
```ruby
def show
@user = authorize User.find(params[:id])
end
```
You can easily get a hold of an instance of the policy through the `policy`
method in both the view and controller. This is especially useful for
conditionally showing links or buttons in the view:
``` erb
<% if policy(@post).update? %>
<%= link_to "Edit post", edit_post_path(@post) %>
<% end %>
```
## Headless policies
Given there is a policy without a corresponding model / ruby class,
you can retrieve it by passing a symbol.
```ruby
# app/policies/dashboard_policy.rb
class DashboardPolicy < Struct.new(:user, :dashboard)
# ...
end
```
Note that the headless policy still needs to accept two arguments. The
second argument will just be the symbol `:dashboard` in this case which
is what is passed as the record to `authorize` below.
```ruby
# In controllers
authorize :dashboard, :show?
```
```erb
# In views
<% if policy(:dashboard).show? %>
<%= link_to 'Dashboard', dashboard_path %>
<% end %>
```
## Scopes
Often, you will want to have some kind of view listing records which a
particular user has access to. When using Pundit, you are expected to
define a class called a policy scope. It can look something like this:
``` ruby
class PostPolicy < ApplicationPolicy
class Scope
attr_reader :user, :scope
def initialize(user, scope)
@user = user
@scope = scope
end
def resolve
if user.admin?
scope.all
else
scope.where(published: true)
end
end
end
def update?
user.admin? or not record.published?
end
end
```
Pundit makes the following assumptions about this class:
- The class has the name `Scope` and is nested under the policy class.
- The first argument is a user. In your controller, Pundit will call the
`current_user` method to retrieve what to send into this argument.
- The second argument is a scope of some kind on which to perform some kind of
query. It will usually be an ActiveRecord class or a
`ActiveRecord::Relation`, but it could be something else entirely.
- Instances of this class respond to the method `resolve`, which should return
some kind of result which can be iterated over. For ActiveRecord classes,
this would usually be an `ActiveRecord::Relation`.
You'll probably want to inherit from the application policy scope generated by the
generator, or create your own base class to inherit from:
``` ruby
class PostPolicy < ApplicationPolicy
class Scope < Scope
def resolve
if user.admin?
scope.all
else
scope.where(published: true)
end
end
end
def update?
user.admin? or not record.published?
end
end
```
You can now use this class from your controller via the `policy_scope` method:
``` ruby
def index
@posts = policy_scope(Post)
end
def show
@post = policy_scope(Post).find(params[:id])
end
```
Like with the authorize method, you can also override the policy scope class:
``` ruby
def index
# publication_class => Post
@publications = policy_scope(publication_class, policy_scope_class: PublicationPolicy::Scope)
end
```
Just as with your policy, this will automatically infer that you want to use
the `PostPolicy::Scope` class, it will instantiate this class and call
`resolve` on the instance. In this case it is a shortcut for doing:
``` ruby
def index
@posts = PostPolicy::Scope.new(current_user, Post).resolve
end
```
You can, and are encouraged to, use this method in views:
``` erb
<% policy_scope(@user.posts).each do |post| %>
<%= link_to post.title, post_path(post) %>
<% end %> ``` ## Ensuring policies and scopes are used When you are developing an application with Pundit it can be easy to forget to authorize some action. People are forgetful after all. Since Pundit encourages you to add the `authorize` call manually to each controller action, it's really easy to miss one. Thankfully, Pundit has a handy feature which reminds you in case you forget. Pundit tracks whether you have called `authorize` anywhere in your controller action. Pundit also adds a method to your controllers called `verify_authorized`. This method will raise an exception if `authorize` has not yet been called. You should run this method in an `after_action` hook to ensure that you haven't forgotten to authorize the action. For example: ``` ruby class ApplicationController < ActionController::Base include Pundit after_action :verify_authorized end ``` Likewise, Pundit also adds `verify_policy_scoped` to your controller. This will raise an exception similar to `verify_authorized`. However, it tracks if `policy_scope` is used instead of `authorize`. This is mostly useful for controller actions like `index` which find collections with a scope and don't authorize individual instances. ``` ruby class ApplicationController < ActionController::Base include Pundit after_action :verify_authorized, except: :index after_action :verify_policy_scoped, only: :index end ``` **This verification mechanism only exists to aid you while developing your application, so you don't forget to call `authorize`. It is not some kind of failsafe mechanism or authorization mechanism. You should be able to remove these filters without affecting how your app works in any way.** Some people have found this feature confusing, while many others find it extremely helpful. If you fall into the category of people who find it confusing then you do not need to use it. Pundit will work just fine without using `verify_authorized` and `verify_policy_scoped`. ### Conditional verification If you're using `verify_authorized` in your controllers but need to conditionally bypass verification, you can use `skip_authorization`. For bypassing `verify_policy_scoped`, use `skip_policy_scope`. 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. ```ruby def show record = Record.find_by(attribute: "value") if record.present? authorize record else skip_authorization end end ``` ## Manually specifying policy classes Sometimes you might want to explicitly declare which policy to use for a given class, instead of letting Pundit infer it. This can be done like so: ``` ruby class Post def self.policy_class PostablePolicy end end ``` ## Just plain old Ruby As you can see, Pundit 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 policy and scope classes are 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 policies. 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 policies: ``` sh rails g pundit:policy post ``` ## 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 policy isn't `nil` for every single permission. Aside from policies, you can add this check to the base class for scopes. We suggest that you define a filter that redirects unauthenticated users to the login page. As a secondary defence, if you've defined an ApplicationPolicy, it might be a good idea to raise an exception if somehow an unauthenticated user got through. This way you can fail more gracefully. ``` ruby class ApplicationPolicy def initialize(user, record) raise Pundit::NotAuthorizedError, "must be logged in" unless user @user = user @record = record end class Scope attr_reader :user, :scope def initialize(user, scope) raise Pundit::NotAuthorizedError, "must be logged in" unless user @user = user @scope = scope end end end ``` ## NilClassPolicy To support a [null object pattern](https://en.wikipedia.org/wiki/Null_Object_pattern) you may find that you want to implement a `NilClassPolicy`. This might be useful where you want to extend your ApplicationPolicy to allow some tolerance of, for example, associations which might be `nil`. ```ruby class NilClassPolicy < ApplicationPolicy class Scope < Scope def resolve raise Pundit::NotDefinedError, "Cannot scope NilClass" end end def show? false # Nobody can see nothing end end ``` ## Rescuing a denied Authorization in Rails Pundit raises a `Pundit::NotAuthorizedError` you can [rescue_from](http://guides.rubyonrails.org/action_controller_overview.html#rescue-from) in your `ApplicationController`. You can customize the `user_not_authorized` method in every controller. ```ruby class ApplicationController < ActionController::Base protect_from_forgery include Pundit rescue_from Pundit::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 ``` Alternatively, you can globally handle Pundit::NotAuthorizedError's by having rails handle them as a 403 error and serving a 403 error page. Add the following to application.rb: ```config.action_dispatch.rescue_responses["Pundit::NotAuthorizedError"] = :forbidden``` ## Creating custom error messages `NotAuthorizedError`s provide information on what query (e.g. `:create?`), what record (e.g. an instance of `Post`), and what policy (e.g. an instance of `PostPolicy`) caused the error to be raised. One way to use these `query`, `record`, and `policy` properties is to connect them with `I18n` to generate error messages. Here's how you might go about doing that. ```ruby class ApplicationController < ActionController::Base rescue_from Pundit::NotAuthorizedError, with: :user_not_authorized private def user_not_authorized(exception) policy_name = exception.policy.class.to_s.underscore flash[:error] = t "#{policy_name}.#{exception.query}", scope: "pundit", default: :default redirect_to(request.referrer || root_path) end end ``` ```yaml en: pundit: default: 'You cannot perform this action.' post_policy: update?: 'You cannot edit this post!' create?: 'You cannot create posts!' ``` Of course, this is just an example. Pundit is agnostic as to how you implement your error messaging. ## Manually retrieving policies and scopes Sometimes you want to retrieve a policy for a record outside the controller or view. For example when you delegate permissions from one policy to another. You can easily retrieve policies and scopes like this: ``` ruby Pundit.policy!(user, post) Pundit.policy(user, post) Pundit.policy_scope!(user, Post) Pundit.policy_scope(user, Post) ``` The bang methods will raise an exception if the policy does not exist, whereas those without the bang will return nil. ## Customize Pundit 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 Pundit. Simply define a method in your controller called `pundit_user`. ```ruby def pundit_user User.find_by_other_means end ``` ## Policy Namespacing In some cases it might be helpful to have multiple policies that serve different contexts for a resource. A prime example of this is the case where User policies differ from Admin policies. To authorize with a namespaced policy, pass the namespace into the `authorize` helper in an array: ```ruby authorize(post) # => will look for a PostPolicy authorize([:admin, post]) # => will look for an Admin::PostPolicy authorize([:foo, :bar, post]) # => will look for a Foo::Bar::PostPolicy policy_scope(Post) # => will look for a PostPolicy::Scope policy_scope([:admin, Post]) # => will look for an Admin::PostPolicy::Scope policy_scope([:foo, :bar, Post]) # => will look for a Foo::Bar::PostPolicy::Scope ``` If you are using namespaced policies for something like Admin views, it can be useful to override the `policy_scope` and `authorize` helpers in your `AdminController` to automatically apply the namespacing: ```ruby class AdminController < ApplicationController def policy_scope(scope) super([:admin, scope]) end def authorize(record, query = nil) super([:admin, record], query) end end class Admin::PostController < AdminController def index policy_scope(Post) end def show post = Post.find(params[:id]) authorize(post) end end ``` ## Additional context Pundit 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. Pundit does not allow you to pass additional arguments to policies 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 policy. ``` ruby class UserContext attr_reader :user, :ip def initialize(user, ip) @user = user @ip = ip end end class ApplicationController include Pundit def pundit_user UserContext.new(current_user, request.ip) end end ``` ## Strong parameters In Rails 4 (or Rails 3.2 with the [strong_parameters](https://github.com/rails/strong_parameters) gem), mass-assignment protection is handled in the controller. With Pundit you can control which attributes a user has access to update via your policies. You can set up a `permitted_attributes` method in your policy like this: ```ruby # app/policies/post_policy.rb class PostPolicy < ApplicationPolicy 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 policy: ```ruby # 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(policy(@post).permitted_attributes) end end ``` However, this is a bit cumbersome, so Pundit provides a convenient helper method: ```ruby # 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 ``` If you want to permit different attributes based on the current action, you can define a `permitted_attributes_for_#{action}` method on your policy: ```ruby # app/policies/post_policy.rb class PostPolicy < ApplicationPolicy def permitted_attributes_for_create [:title, :body] end def permitted_attributes_for_edit [:body] end end ``` If you have defined an action-specific method on your policy for the current action, the `permitted_attributes` helper will call it instead of calling `permitted_attributes` on your controller. If you need to fetch parameters based on namespaces different from the suggested one, override the below method, in your controller, and return an instance of `ActionController::Parameters`. ```ruby def pundit_params_for(record) params.require(PolicyFinder.new(record).param_key) end ``` For example: ```ruby # If you don't want to use require def pundit_params_for(record) params.fetch(PolicyFinder.new(record).param_key, {}) end # If you are using something like the JSON API spec def pundit_params_for(_record) params.fetch(:data, {}).fetch(:attributes, {}) end ``` ## RSpec ### Policy Specs Pundit includes a mini-DSL for writing expressive tests for your policies in RSpec. Require `pundit/rspec` in your `spec_helper.rb`: ``` ruby require "pundit/rspec" ``` Then put your policy specs in `spec/policies`, and make them look somewhat like this: ``` ruby describe PostPolicy do subject { described_class } permissions :update?, :edit? do it "denies access if post is published" do expect(subject).not_to permit(User.new(admin: false), Post.new(published: true)) end it "grants access if post is published and user is an admin" do expect(subject).to permit(User.new(admin: true), Post.new(published: true)) end it "grants access if post is unpublished" do expect(subject).to permit(User.new(admin: false), Post.new(published: false)) end end end ``` An alternative approach to Pundit policy specs is scoping them to a user context as outlined in this [excellent post](http://thunderboltlabs.com/blog/2013/03/27/testing-pundit-policies-with-rspec/) and implemented in the third party [pundit-matchers](https://github.com/chrisalley/pundit-matchers) gem. ### Scope Specs Pundit does not provide a DSL for testing scopes. Just test it like a regular Ruby class! # External Resources - [RailsApps Example Application: Pundit and Devise](https://github.com/RailsApps/rails-devise-pundit) - [Migrating to Pundit from CanCan](http://blog.carbonfive.com/2013/10/21/migrating-to-pundit-from-cancan/) - [Testing Pundit Policies with RSpec](http://thunderboltlabs.com/blog/2013/03/27/testing-pundit-policies-with-rspec/) - [Using Pundit outside of a Rails controller](https://github.com/varvet/pundit/pull/136) - [Straightforward Rails Authorization with Pundit](http://www.sitepoint.com/straightforward-rails-authorization-with-pundit/) ## Other implementations - [Flask-Pundit](https://github.com/anurag90x/flask-pundit) (Python) is a [Flask](http://flask.pocoo.org/) extension "heavily inspired by" Pundit # License Licensed under the MIT license, see the separate LICENSE.txt file.