🛡 Terminator 🛡

Terminator is toolkit for granular ability management for performers. It allows you to define granular abilities such as:

• Performer -> Ability
• Performer -> [Ability, Ability, ...]
• Role -> [Ability, Ability, ...]
• Performer -> Role -> [Ability, Ability, Ability]
• Performer -> [Role -> [Ability], Role -> [Ability, ...]]
• Performer -> AnyEntity -> [Ability, ...]

It tries to mimic https://en.wikipedia.org/wiki/Attribute-based_access_control and allow to define any policy which is needed.

Here is a small example:

defmodule Sample.Post
  use Terminator

  def delete_post(id) do
    performer = Sample.Repo.get(Terminator.Performer, 1)
    load_and_authorize_performer(performer)
    post = %Post{id: 1}

    permissions do
      has_role(:admin) # or
      has_role(:editor) # or
      has_ability(:delete_posts) # or
      has_ability(:delete, post) # Entity related abilities
      calculated(fn performer ->
        performer.email_confirmed?
      end)
    end

    as_authorized do
      Sample.Repo.get(Sample.Post, id) |> Sample.repo.delete()
    end

    # Notice that you can use both macros or functions

    case is_authorized? do
      :ok -> Sample.Repo.get(Sample.Post, id) |> Sample.repo.delete()
      {:error, message} -> "Raise error"
      _ -> "Raise error"
    end
  end

Features

• Performer -> [Ability] permission schema
• Role -> [Ability] permission schema
• Performer -> [Role] -> [Ability] permission schema
• Performer -> Object -> [Ability] permission schema
• Computed permission in runtime
• Easily readable DSL
• ueberauth integration
• absinthe middleware
• Session plug to get current_user

Installation

def deps do
  [
    {:terminator, "~> 0.5.2"}
  ]
end

# In your config/config.exs file
config :terminator, Terminator.Repo,
  username: "postgres",
  password: "postgres",
  database: "terminator_dev",
  hostname: "localhost"

iex> mix terminator.setup

Usage with ecto

Terminator is originally designed to be used with Ecto. Usually you will want to have your own table for Accounts/Users living in your application. To do so you can link performer with belongs_to association within your schema.

# In your migrations add performer_id field
defmodule Sample.Migrations.CreateUsersTable do
  use Ecto.Migration

  def change do
    create table(:users) do
      add :username, :string
      add :performer_id, references(Terminator.Performer.table())

      timestamps()
    end

    create unique_index(:users, [:username])
  end
end

This will allow you link any internal entity with 1-1 association to performers. Please note that you need to create performer on each user creation (e.g with Terminator.Performer.changeset/2) and call put_assoc inside your changeset

# In schema defintion
defmodule Sample.User do
  use Ecto.Schema

  schema "users" do
    field :username, :String

    belongs_to :performer, Terminator.Performer

    timestamps()
  end
end

# In your model
defmodule Sample.Post
  use Terminator

  def delete_post(id) do
    user = Sample.Repo.get(Sample.User, 1)
    load_and_authorize_performer(user)
    # Function allows multiple signatues of performer it can
    # be either:
    #  * %Terminator.Performer{}
    #  * %AnyStruct{performer: %Terminator.Performer{}}
    #  * %AnyStruct{performer_id: id} (this will perform database preload)


    permissions do
      has_role(:admin) # or
      has_role(:editor) # or
      has_ability(:delete_posts) # or
    end

    as_authorized do
      Sample.Repo.get(Sample.Post, id) |> Sample.repo.delete()
    end

    # Notice that you can use both macros or functions

    case is_authorized? do
      :ok -> Sample.Repo.get(Sample.Post, id) |> Sample.repo.delete()
      {:error, message} -> "Raise error"
      _ -> "Raise error"
    end
  end

Terminator tries to infer the performer, so it is easy to pass any struct (could be for example User in your application) which has set up belongs_to association for performer. If the performer was already preloaded from database Terminator will take it as loaded performer. If you didn't do preload and just loaded User -> Repo.get(User, 1) Terminator will fetch the performer on each authorization try.

Calculated permissions

Often you will come to case when static permissions are not enough. For example allow only users who confirmed their email address.

defmodule Sample.Post do
  def create() do
    user = Sample.Repo.get(Sample.User, 1)
    load_and_authorize_performer(user)

    permissions do
      calculated(fn performer -> do
        performer.email_confirmed?
      end)
    end
  end
end

We can also use DSL form of calculated keyword

defmodule Sample.Post do
  def create() do
    user = Sample.Repo.get(Sample.User, 1)
    load_and_authorize_performer(user)

    permissions do
      calculated(:confirmed_email)
    end
  end

  def confirmed_email(performer) do
    performer.email_confirmed?
  end
end

Composing calculations

When we need to performer calculation based on external data we can invoke bindings to calculated/2

defmodule Sample.Post do
  def create() do
    user = Sample.Repo.get(Sample.User, 1)
    post = %Post{owner_id: 1}
    load_and_authorize_performer(user)

    permissions do
      calculated(:confirmed_email)
      calculated(:is_owner, [post])
    end
  end

  def confirmed_email(performer) do
    performer.email_confirmed?
  end

  def is_owner(performer, [post]) do
    performer.id == post.owner_id
  end
end

To perform exclusive abilities such as when User is owner of post AND is in editor role we can do so as in following example

defmodule Sample.Post do
  def create() do
    user = Sample.Repo.get(Sample.User, 1)
    post = %Post{owner_id: 1}
    load_and_authorize_performer(user)

    permissions do
      has_role(:editor)
    end

    as_authorized do
      case is_owner(performer, post) do
        :ok -> ...
        {:error, message} -> ...
      end
    end
  end

  def is_owner(performer, post) do
    load_and_authorize_performer(performer)

    permissions do
      calculated(fn p, [post] ->
        p.id == post.owner_id
      end)
    end

    is_authorized?
  end
end

We can simplify example in this case by excluding DSL for permissions

defmodule Sample.Post do
  def create() do
    user = Sample.Repo.get(Sample.User, 1)
    post = %Post{owner_id: 1}

    # We can also use has_ability?/2
    if has_role?(user, :admin) and is_owner(user, post) do
      ...
    end
  end

  def is_owner(performer, post) do
    performer.id == post.owner_id
  end
end

Entity related abilities

Terminator allows you to grant abilities on any particular struct. Struct needs to have signature of %{__struct__: entity_name, id: entity_id} to infer correct relations. Lets assume that we want to grant :delete ability on particular Post for our performer:

iex> {:ok, performer} = %Terminator.Performer{} |> Terminator.Repo.insert()
iex> post = %Post{id: 1}
iex> ability = %Ability{identifier: "delete"}
iex> Terminator.Performer.grant(performer, :delete, post)
iex> Terminator.has_ability?(performer, :delete, post)
true

defmodule Sample.Post do
  def delete() do
    user = Sample.Repo.get(Sample.User, 1)
    post = %Post{id: 1}
    load_and_authorize_performer(user)

    permissions do
      has_ability(:delete, post)
    end

    as_authorized do
      :ok
    end
  end
end

Granting abilities

Let's assume we want to create new Role - admin which is able to delete accounts inside our system. We want to have special Performer who is given this role but also he is able to have Ability for banning users.

1. Create performer

iex> {:ok, performer} = %Terminator.Performer{} |> Terminator.Repo.insert()

2. Create some abilities

iex> {:ok, ability_delete} = Terminator.Ability.build("delete_accounts", "Delete accounts of users") |> Terminator.Repo.insert()
iex> {:ok, ability_ban} = Terminator.Ability.build("ban_accounts", "Ban users") |> Terminator.Repo.insert()

3. Create role

iex> {:ok, role} = Terminator.Role.build("admin", [], "Site administrator") |> Terminator.Repo.insert()

4. Grant abilities to a role

iex> Terminator.Role.grant(role, ability_delete)

5. Grant role to a performer

iex> Terminator.Performer.grant(performer, role)

6. Grant abilities to a performer

iex> Terminator.Performer.grant(performer, ability_ban)

iex> performer |> Terminator.Repo.preload([:roles, :abilities])
%Terminator.Performer{
  abilities: [
    %Terminator.Ability{
      identifier: "ban_accounts"
    }
  ]
  roles: [
    %Terminator.Role{
      identifier: "admin"
      abilities: ["delete_accounts"]
    }
  ]
}

Revoking abilities

Same as we can grant any abilities to models we can also revoke them.

iex> Terminator.Performer.revoke(performer, role)
iex> performer |> Terminator.Repo.preload([:roles, :abilities])
%Terminator.Performer{
  abilities: [
    %Terminator.Ability{
      identifier: "ban_accounts"
    }
  ]
  roles: []
}
iex> Terminator.Performer.revoke(performer, ability_ban)
iex> performer |> Terminator.Repo.preload([:roles, :abilities])
%Terminator.Performer{
  abilities: []
  roles: []
}

License

MIT © Milos Mosovsky