View Source Janus (Janus v0.1.0)

Flexible and composable authorization for resources defined by an Ecto.Schema.

Janus provides an API for defining authorization policies that can be used both as filters in Ecto queries and to authorize actions on loaded resources with minimal to no duplication of authorization logic.

Janus is split into two primary components:

  • Janus.Policy - functions and behaviour for defining policy modules, which describe the allowed actors, actions, and resources in your application. This is where you look if you're writing a policy module.
  • Janus.Authorization - functions and behaviour used by the rest of your application to authorize and load resources. This is where you look if you're using a policy module.

Janus defines a Mix task to generate the basic policy module that will get you started:

$ mix janus.gen.policy

policies

Policies

Policy modules are created by invoking use Janus, which implements both the Janus.Policy and Janus.Authorization behaviours:

defmodule Policy do
  use Janus

  @impl true
  def policy_for(policy, _user) do
    policy
  end
end

When you invoke use Janus, default implementations are injected for required callbacks, except for Janus.Policy.policy_for/2. This callback is your foundation, as it returns the authorization policy for an individual user of your application.

The policy above is not very useful -- it doesn't allow anyone to do anything -- but that can be changed by using the Janus.Policy API to define actions, resources, and conditions that make up your authorization rules.

def policy_for(policy, %User{role: :moderator} = mod) do
  policy
  |> allow(:read, Post)
  |> allow([:edit, :archive, :unarchive], Post, where: [user: [role: :member]])
  |> allow([:edit, :archive, :unarchive], Post, where: [user_id: mod.id])
  |> deny(:unarchive, Post, where: [archived_by: [role: :admin]])
end

See the Janus.Policy documentation for more on defining policies.

authorization

Authorization

With our policy module defined, it can now be used to load and authorize resources.

iex> Policy.authorize(some_post, :archive, moderator)
{:ok, some_post}

iex> Policy.authorize(post_archived_by_admin, :unarchive, moderator)
:error

iex> Policy.filter_authorized(Post, :read, moderator)
%Ecto.Query{}

iex> Policy.filter_authorized(Post, :read, moderator) |> Repo.all()
[ ... posts the moderator can read ]

iex> Policy.any_authorized?(Post, :edit, moderator)
true # there are rules allowing moderators to edit posts

iex> Policy.any_authorized?(Post, :delete, moderator)
false # there are no rules that allow moderators to delete posts

These functions make up the Janus.Authorization behaviour, and their definitions were injected by default when we invoked use Janus. This is the "public API" that the rest of your application will use to authorize resources.

See the Janus.Authorization documentation for more.

integration-with-ecto

Integration with Ecto

The primary assumption that Janus makes is that your resources are backed by an Ecto.Schema. Using Ecto's schema reflection capabilities, Janus is able to use the same policy to authorize a single resource and to construct a composable Ecto query that is aware of field types and associations.

# This query would result in the 5 latest posts that the current
# user is authorized to see, preloaded with the user # who made
# the post (but only if the current user is  allowed to see that
# user).

Post
|> Policy.filter_authorized(:read, current_user,
  preload_authorized: :user
)
|> order_by(desc: :inserted_at)
|> limit(5)

This integration with Ecto queries is main reason Janus exists.

Link to this section Summary

Functions

Sets up a module to implement the Janus.Policy and Janus.Authorization behaviours.

Link to this section Types

@type action() :: any()
@type actor() :: any()
@type schema_module() :: module()

Link to this section Functions

Link to this macro

__using__(opts)

View Source (macro)

Sets up a module to implement the Janus.Policy and Janus.Authorization behaviours.

Invoking use Janus does the following:

  • invokes use Janus.Policy which imports functions for defining policies and injects wrapper definitions for policy_for/1 and policy_for/2 that support hooks (see Janus.Policy for more)
  • injects implementations for the Janus.Authorization behaviour

example

Example

defmodule MyApp.Policy do
  use Janus

  @impl true
  def policy_for(policy, _actor) do
    policy
  end
end

# imports `authorize`, `filter_authorized`, and `any_authorized?`
use MyApp.Policy