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Pundit

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Pundit provides a set of helpers which guide you in leveraging regular Elixir methods to build a simple authorization system. This library is based heavily on Jonas Nicklas' Ruby project of the same name.

Simple Elixir functions are defined for a given struct and allow you to encapsulate authentication logic. You can use this code within a module that is an Ecto.Schema, but that's not necessary (Ecto isn't required). The action names are taken from the list of actions defined by Phoenix controllers.

Installation

To install Pundit, just add an entry to your mix.exs:

def deps do
  [
    # ...
    {:pundit, "~> 1.0"}
  ]
end

(Check Hex to make sure you're using an up-to-date version number.)

Usage

Here's a basic example, starting with a simple struct for a Post. A module named Post.Policy should be created to encapsulate all of the access methods (Pundit will automatically look for the <struct module>.Policy module to determine the module name to look at for access methods).

To declare an initial set of access functions (show?, edit?, delete?, etc) which all return false (default safe!), just use Pundit.DefaultPolicy. You can then override the functions as needed with the logic necessary to determine whether a user should be able to perform the given action. In this example, we only determine whether a user can edit? a post, leaving all other functions (like delete?) to return the default of false.

defmodule Post do
  defstruct [:author, :title, :body, :comments]

  defmodule Policy do
    # This will initialize all the action functions, all of which return false
    # by default. Override them individually to return true when they should,
    # like edit? is overriden below.
    use Pundit.DefaultPolicy

    def edit?(post, user) do
      user.name == post.author
    end
  end
end

post = %Post{author: "Snake Plissken"}
author = %{name: "Snake Plissken"}
# next line is same as Pundit.can?(post, author, :edit?)
# Pundit will just delegate to Post.Policy.edit?(post, user)
if Pundit.edit?(post, author) do
  IO.puts("Can edit!")
end

if Pundit.delete?(post, author) do
  IO.puts("This line should never be called")
end

# raise exception if user should be able to do a thing
Pundit.authorize!(post, author, :edit?)

Scope

You can also provide query scope for a struct (say, if you're using Ecto.Schema) for a given user. For instance, say our Post was an Ecto schema. Our function for scoping all Posts to a specific User could be to find all Posts that were authored by a user. For instance:

defmodule Post do
  use Ecto.Schema
  import Ecto.Query, only: [from: 2]

  defmodule Policy do
    use Pundit.DefaultPolicy
          
    def scope(query, user) do
      from post in query,
        where: post.author_id == ^user.id
    end
  end
end

user = MyApp.Repo.get(User, 1)
posts = Pundit.scope(Post, user) |> Repo.all()

query = from p in Post, where: p.comment_count > 10
popular_posts = Pundit.scope(query, user) |> Repo.all()

See the docs for more examples.

Running Tests

To run tests:

$ mix test

Reporting Issues

Please report all issues on github.


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