Guardian

An authentication framework for use with Elixir applications.

Guardian is based on similar ideas to Warden and Omniauth but is re-imagined for modern systems where Elixir manages the authentication requirements.

Guardian remains a functional system. It integrates with Plug, but can be used outside of it. If you're implementing a TCP/UDP protocol directly, or want to utilize your authentication via channels, Guardian is your friend.

The core currency of authentication in Guardian is JWT. You can use the JWT to authenticate web endpoints, channels, and TCP sockets and it can contain any authenticated assertions that the issuer wants to include.

Installation

Guardian relies on Joken. You'll need to install and configure Joken for your application.

Add Guardian to your application

mix.deps

defp deps do
  [
    # ...
    {:guardian, "~> 0.6.2"}
    # ...
  ]
end

config.exs

config :joken, config_module: Guardian.JWT

config :guardian, Guardian,
  issuer: "MyApp",
  ttl: { 30, :days },
  verify_issuer: true,
  secret_key: <guardian secret key>,
  serializer: MyApp.GuardianSerializer

Serializer

The serializer knows how to encode and decode your resource into and out of the token. A simple serializer:

defmodule MyApp.GuardianSerializer do
  @behaviour Guardian.Serializer

  alias MyApp.Repo
  alias MyApp.User

  def for_token(user = %User{}), do: { :ok, "User:#{user.id}" }
  def for_token(_), do: { :error, "Unknown resource type" }

  def from_token("User:" <> id), do: { :ok, Repo.get(User, id) }
  def from_token(_), do: { :error, "Unknown resource type" }
end

Plug API

Guardian ships with some plugs to help integrate into your application.

Guardian.Plug.VerifySession

Looks for a token in the session. Useful for browser sessions. If one is not found, this does nothing.

Guardian.Plug.VerifyHeader

Looks for a token in the Authorization header. Useful for apis. If one is not found, this does nothing.

Guardian.Plug.EnsureAuthenticated

Looks for a previously verified token. If one is found, continues, otherwise it will call the :on_failure function.

When you ensure a session, you must declare an error handler. This can be done as part of a pipeline or inside a pheonix controller.

defmodule MyApp.MyController do
  use MyApp.Web, :controller

  plug Guardian.Plug.EnsureAuthenticated, on_failure: { MyApp.MyController, :unauthenticated }
end

The failure function must receive the connection, and the connection params.

Guardian.Plug.EnsurePermissions

Looks for a previously verified token. If one is found, confirms that all listed permissions are present in the token. If not, the failure function is called.

defmodule MyApp.MyController do
  use MyApp.Web, :controller

  plug Guardian.Plug.EnsurePermissions, on_failure: { MyApp.MyController, :forbidden }, default: [:read, :write]
end

Pipelines

These plugs can be used to construct pipelines in Phoenix.

pipeline :browser_session do
  plug Guardian.Plug.VerifySession
  plug Guardian.Plug.LoadResource
end

pipeline :api do
  plug :accepts, ["json"]
  plug Guardian.Plug.VerifyHeader
  plug Guardian.Plug.LoadResource
end

scope "/", MyApp do
  pipe_through [:browser, :browser_session] # Use the default browser stack
  # ...
end

scope "/api", MyApp.Api do
  pipe_through [:api] # Use the default browser stack
end

From here, you can either EnsureAuthenticated in your pipeline, or on a per-controller basis.

defmodule MyApp.MyController do
  use MyApp.Web, :controller

  plug Guardian.Plug.EnsureAuthenticated, on_failure: { MyApp.MyHandler, :unauthenticated }
end

Sign in and Sign out

It's up to you how you verify the claims to encode into the token Guardian uses. As an example, here's the important parts of a SessionController

defmodule MyApp.SessionController do
  use MyApp.Web, :controller

  alias MyApp.User
  alias MyApp.UserQuery

  plug :scrub_params, "user" when action in [:create]

  def create(conn, params = %{}) do
    conn
    |> put_flash(:info, "Logged in.")
    |> Guardian.Plug.sign_in(verified_user) # verify your logged in resource
    |> redirect(to: user_path(conn, :index))
  end

  def delete(conn, _params) do
    Guardian.Plug.sign_out(conn)
    |> put_flash(:info, "Logged out successfully.")
    |> redirect(to: "/")
  end
end

Guardian.Plug.sign_in

You can sign in with a resource (that the serializer knows about)

Guardian.Plug.sign_in(conn, user) # Sign in with the default storage

Guardian.Plug.sign_in(conn, user, :token, claims)  # give some claims to use for the token jwt

Guardian.Plug.sign_in(conn, user, :token, key: :secret)  # create a token in the :secret location

To attach permissions to the token, use the :perms key and pass it a map. Note. To add permissions, you should configure them in your guardian config.

Guardian.Plug.sign_in(conn, user, :token, perms: %{ default: [:read, :write], admin: [:all] })

Guardian.Plug.sign_in(conn, user, :token, key: :secret, perms: %{ default: [:read, :write], admin: [:all]})  # create a token in the :secret location

Guardian.Plug.sign_out

Guardian.Plug.sign_out(conn) # Sign out everything (clear session)

Guardian.Plug.sign_out(conn, :secret) # Clear the token and associated user from the 'secret' location

Current resource, token and claims

Access to the current resource, token and claims is useful. Note, you'll need to have run the VerifySession/Header for token and claim access, and LoadResource to access the resource.

Guardian.Plug.claims(conn) # Access the claims in the default location
Guardian.Plug.claims(conn, :secret) # Access the claims in the secret location

Guardian.Plug.current_token(conn) # access the token in the default location
Guardian.Plug.current_token(conn, :secret) # access the token in the secret location

For the resource

Guardian.Plug.current_resource(conn) # Access the loaded resource in the default location
Guardian.Plug.current_resource(conn, :secret) # Access the loaded resource in the secret location

Without Plug

There are many instances where Plug might not be in use. Channels, and raw sockets for e.g. If you need to do things your own way.

{ :ok, jwt, encoded_claims } = Guardian.encode_and_sign(resource, <token_type>, claims_map)

This will give you a new JWT to use with the claims ready to go. The token type is encoded into the JWT as the 'aud' field and is intended to be used as the type of token.

{ :ok, jwt, full_claims } = Guardian.encode_and_sign(resource, :token)

Add some permissions

{ :ok, jwt, full_claims } = Guardian.encode_and_sign(resource, :token, perms: %{ default: [:read, :write], admin: Guardian.Permissions.max})

Currently suggested token types are:

"token" - Use for API or CORS access. These are basic tokens.

You can also customize the claims you're asserting.

claims = Guardian.Claims.app_claims
         |> Dict.put(:some_claim, some_value)
         |> Guardian.Claims.ttl({3, :days})

{ :ok, jwt, full_claims } = Guardian.encode_and_sign(resource, :token, claims)

To verify the token:

case Guardian.decode_and_verify(jwt) do
  { :ok, claims } -> do_things_with_claims(claims)
  { :error, reason } -> do_things_with_an_error(reason)
end

Accessing the resource from a set of claims:

case Guardian.serializer.from_token(claims.sub) do
  { :ok, resource } -> do_things_with_resource(resource)
  { :error, reason } -> do_things_without_a_resource(reason)
end

Permissions

Guardian includes support for including permissions. Declare your permissions in your configuration. All known permissions must be included.

config :guardian, Guardian,
       permissions: %{
         default: [:read, :write],
         admin: [:dashboard, :reconcile]
       }

JWTs need to be kept reasonably small so that they can fit into an authorization header. For this reason, permissions are encded as bits (an integer) in the token. You can have up to 64 permissions per set, and as many sets as you like. In the example above, we have the :default set, and the :admin set.

The bit value of the permissions within a set is determined by it's position in the config.

# Fetch permissions from the claims map

Guardian.Permissions.from_claims(claims, :default)
Guardian.Permissions.from_claims(claims, :admin)

# Check the permissions for all present

Guardian.Permissions.from_claims(claims, :default) |> Guardian.Permissions.all?([:read, :write], :default)
Guardian.Permissions.from_claims(claims, :admin) |> Guardian.Permissions.all?([:reconcile], :admin)

# Check for any permissions
Guardian.Permissions.from_claims(claims, :default) |> Guardian.Permissions.any?([:read, :write], :default)
Guardian.Permissions.from_claims(claims, :admin) |> Guardian.Permissions.any?([:reconcile, :dashboard], :admin)

You can use a plug to ensure permissions are present. See Guardian.Plug.EnsurePermissions

Setting permissions

When you generate (or sign in) a token, you can inject permissions into it.

Guardian.encode_and_sign(resource, :token, perms: %{ admin: [:dashaboard], default: Guardian.Permissions.max}})

By setting a permission using Guardian.Permission.max you're setting all the bits, so even if new permissions are added, they will be set.

You can similarly pass a :perms key to the sign_in method to have the permissions encoded into the token.

Hooks

Often you'll need to take action on some event within the lifecycle of authentication. Recording logins etc. Guardian provides hooks to allow you to do this. Use the Guardian.Hooks module to setup. Default implementations are available for all callbacks.

defmodule MyApp.GuardianHooks do
  use Guardian.Hooks

  def after_sign_in(conn, location) do
    user = Guardian.Plug.current_resource(conn, location)
    IO.puts("SIGNED INTO LOCATION WITH: #{user.email}")
    conn
  end
end

By default, JWTs are not tracked. This means that after 'logout' the token can still be used if it is stored outside the system. This is because Guardian does not track tokens and only interprates them live. When using Guardian in this way, be sure you consider the expiry time as this is one of the few options you have to make your tokens invalid.

If you want more control over this you should implement a hook that tracks the tokens in some storage. When calling Guardian.revoke! (called automatically with sign_out).

To keep track of all tokens and ensure they're revoked on sign out you can use GuardianDb. This is a simple Guardian.Hooks module that implements database integration.

config :guardian, Guardian,
       hooks: GuardianDb

config :guardian_db, GuardianDb, repo: MyRepo

Configure Guardian to know which module to use.

config :guardian, Guardian,
       hooks: MyApp.GuardianHooks,
       #…

Phoenix Channels

Guardian uses JWTs to make the integration of authentication management as seamless as possible. Channel integration is part of that.

defmodule MyApp.UsersChannel do
  use Phoenix.Channel
  use Guardian.Channel

  def join(_room, %{ claims: claims, resource: resource }, socket) do
    { :ok, %{ message: "Joined" }, socket }
  end

  def join(room, _, socket) do
    { :error,  :authentication_required }
  end

  def handle_in("ping", _payload, socket) do
    user = Guardian.Channel.current_resource(socket)
    broadcast socket, "pong", %{ message: "pong", from: user.email }
    { :noreply, socket }
  end
end

Guardian picks up on joins that have been made and automatically verifies the token and makes available the claims and resource making the request.

let socket = new Socket("/ws");
socket.connect();
let guardianToken = jQuery('meta[name="guardian_token"]').attr('content');
let chan = socket.chan("pings", { guardian_token: guardianToken });

How to get the tokens onto the page?

<%= if Guardian.Plug.current_token(@conn) do %>
  <meta name='guardian_token' content="<%= Guardian.Plug.current_token(@conn) %>">
<% end %>

Acknowledgements

Many thanks to Sonny Scroggin (@scrogson) for the name Guardian and great feedback to get up and running.

drouchy/guardian