Pundit
Pundit provides a set of helpers which guide you in leveraging regular Ruby classes and object oriented design patterns to build a simple, robust and scalable authorization system.
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Installation
gem "pundit"
Include Pundit in your application controller:
class ApplicationController < ActionController::Base
include Pundit
end
Optionally, you can run the generator, which will set up an application policy with some useful defaults for you:
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 This is a simple example that allows updating a post if the user is an admin, or if the post is unpublished:
class PostPolicy
attr_reader :user, :post
def initialize(user, post)
@user = user
@post = post
end
def update?
user.admin? || !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_usermethod 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:
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:
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:
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:
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:
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:
class PostPolicy < ApplicationPolicy
def admin_list?
user.admin?
end
end
Controller:
def admin_list
authorize Post # we don't have a particular post to authorize
# Rest of controller action
end
authorize returns the instance passed to it, so you can chain it like this:
Controller:
def show
@user = authorize User.find(params[:id])
end
# return the record even for namespaced policies
def show
@user = authorize [:admin, 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:
<% 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.
# 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.
# In controllers
authorize :dashboard, :show?
# 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:
class PostPolicy < ApplicationPolicy
class Scope
def initialize(user, scope)
@user = user
@scope = scope
end
def resolve
if user.admin?
scope.all
else
scope.where(published: true)
end
end
private
attr_reader :user, :scope
end
def update?
user.admin? or not record.published?
end
end
Pundit makes the following assumptions about this class:
- The class has the name
Scopeand is nested under the policy class. - The first argument is a user. In your controller, Pundit will call the
current_usermethod 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 anActiveRecord::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:
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:
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:
def index
# publication_class => Post
@publications = policy_scope(publication_class, policy_scope_class: PublicationPolicy::Scope)
end
In this case it is a shortcut for doing:
def index
@publications = PublicationPolicy::Scope.new(current_user, Post).resolve
end
You can, and are encouraged to, use this method in views:
<% policy_scope(@user.posts).each do |post| %>
<p><%= link_to post.title, post_path(post) %></p>
<% 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:
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.
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.
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:
class Post
def self.policy_class
PostablePolicy
end
end
Alternatively, you can declare an instance method:
class Post
def 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:
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.
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 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.
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 in your ApplicationController. You can customize the user_not_authorized method in every controller.
class ApplicationController < ActionController::Base
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
NotAuthorizedErrors 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.
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
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:
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.
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:
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:
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 = authorize Post.find(params[:id])
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.
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, 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:
# 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:
# 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:
# 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:
# 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.
def pundit_params_for(record)
params.require(PolicyFinder.new(record).param_key)
end
For example:
# 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:
require "pundit/rspec"
Then put your policy specs in spec/policies, and make them look somewhat like this:
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 and implemented in the third party 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
- Migrating to Pundit from CanCan
- Testing Pundit Policies with RSpec
- Testing Pundit with Minitest
- Using Pundit outside of a Rails controller
- Straightforward Rails Authorization with Pundit
Other implementations
- Flask-Pundit (Python) is a Flask extension "heavily inspired by" Pundit
License
Licensed under the MIT license, see the separate LICENSE.txt file.
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