Guardian

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From Github Readme

Guardian

An authentication framework for use with Elixir applications.

Guardian is based on similar ideas to Warden 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 JSON Web Tokens (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

Add Guardian to your application

mix.deps

defp deps do
  [
    # ...
    {:guardian, "~> 0.10.0"}
    # ...
  ]
end

config.exs

config :guardian, Guardian,
  allowed_algos: ["HS512"], # optional
  verify_module: Guardian.JWT,  # optional
  issuer: "MyApp",
  ttl: { 30, :days },
  verify_issuer: true, # optional
  secret_key: <guardian secret key>,
  serializer: MyApp.GuardianSerializer

The items in the configuration allow you to tailor how the JWT generation behaves.

  • allowed_algos - The list of algorithms (must be compatible with JOSE). The first is used as the encoding key. Default is: ["HS512"]
  • verify_module - Provides a mechanism to setup your own validations for items in the token. Default is Guardian.JWT
  • issuer - The entry to put into the token as the issuer. This can be used in conjunction with verify_issuer
  • ttl - The default ttl of a token
  • verify_issuer - If set to true, the issuer will be verified to be the same issuer as specified in the issuer field
  • secret_key - The key to sign the tokens. See below for examples.
  • serializer The serializer that serializes the ‘sub’ (Subject) field into and out of the token.

Secret Key

By specifying a binary, the default behavior is to treat the key as an "oct" key type (short for octet sequence). This key type may be used with the "HS256", "HS384", and "HS512" signature algorithms.

Alternatively, a Map, Function, or %JOSE.JWK{} Struct may be specified for other key types. A full list of example key types is available here.

See the key generation docs from jose for how to generate your own keys.

## Map ##

config :guardian, Guardian,
  allowed_algos: ["ES512"],
  secret_key: %{
    "crv" => "P-521",
    "d" => "axDuTtGavPjnhlfnYAwkHa4qyfz2fdseppXEzmKpQyY0xd3bGpYLEF4ognDpRJm5IRaM31Id2NfEtDFw4iTbDSE",
    "kty" => "EC",
    "x" => "AL0H8OvP5NuboUoj8Pb3zpBcDyEJN907wMxrCy7H2062i3IRPF5NQ546jIJU3uQX5KN2QB_Cq6R_SUqyVZSNpIfC",
    "y" => "ALdxLuo6oKLoQ-xLSkShv_TA0di97I9V92sg1MKFava5hKGST1EKiVQnZMrN3HO8LtLT78SNTgwJSQHAXIUaA-lV"
  }

## Function ##
# If, for example, you have your secret key stored externally (in this example, we're using Redix).

config :guardian, Guardian,
  allowed_algos: ["RS512"],
  secret_key: fn ->
    # Bad practice for example purposes only.
    # An already established connection should be used and possibly cache the value locally.
    {:ok, conn} = Redix.start_link
    rsa_jwk = conn
      |> Redix.command!(["GET my-rsa-key"])
      |> JOSE.JWK.from_binary
    Redix.stop(conn)
    rsa_jwk
  end

## %JOSE.JWK{} Struct ##
# Useful if you store your secret key in an encrypted JSON file with the passphrase in an environment variable.

config :guardian, Guardian,
  allowed_algos: ["Ed25519"],
  secret_key: System.get_env("SECRET_KEY_PASSPHRASE") |> JOSE.JWK.from_file(System.get_env("SECRET_KEY_FILE"))

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 :unauthenticated function of your handler.

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

Guardian.Plug.LoadResource

Up to now the other plugs have been just looking for valid tokens in various places or making sure that the token has the correct permissions.

The LoadResource plug looks in the sub field of the token, fetches the resource from the Serializer and makes it available via Guardian.Plug.current_resource(conn)

Note that this does not ensure a resource will be loaded. If there is no available resource (because it could not be found) current_resource will return nil.

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

  plug Guardian.Plug.EnsureAuthenticated, handler: MyApp.MyAuthErrorHandler
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 :unauthorized function is called on your handler.

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

  plug Guardian.Plug.EnsurePermissions, handler: MyApp.MyAuthErrorHandler, 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, handler: MyApp.MyAuthHandler
end

Sign in and Sign out

It’s up to you how you generate the claims to encode into the token Guardian uses. As an example, here are 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 used 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 ‘typ’ 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
         |> Map.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 encoded 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: [:dashboard], 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 interprets 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,
       #…

Refreshing Tokens

You can use Guardian to refresh tokens. This keeps most of the information in the token intact, but changes the iat, exp, jti and nbf fields.

case Guardian.refresh!(existing_jwt, existing_claims, %{ttl: {15, :days}}) do
  {:ok, new_jwt, new_claims} -> do_things(new_jwt)
  {:error, reason} -> handle_error(reason)
end

Once the new token is created, the old one is revoked before returning the new token.

Phoenix Controllers

Guardian provides some helpers for you to use with your controllers.

Provides a simple helper to provide easier access to the current user and their claims.

defmodule MyApp.MyController do
  use MyApp.Web, :controller
  use Guardian.Phoenix.Controller

  def index(conn, params, user, claims) do
    # do stuff in here
  end
end

You can specify the key location of the user if you’re using multiple locations to store users.

defmodule MyApp.MyController do
  use MyApp.Web, :controller
  use Guardian.Phoenix.Controller, key: :secret

  def index(conn, params, user, claims) do
  # do stuff with the secret user
  end
end

Phoenix Sockets

Guardian provides integration into the Phoenix channels API to provide authentication. You can choose to authenticate either on connect or every time someone joins a topic.

To authenticate the initial connect there’s a couple of options.

  1. Automatically authenticate
  2. Authenticate with more control manually.

To automatically authenticate use the Guardian.Phoenix.Socket module in your socket.

defmodule MyApp.UsersSocket do
  use Phoenix.Socket
  use Guardian.Phoenix.Socket

  def connect(_params, socket) do
    # if we get here, we did not authenticate
    :error
  end
end

Connection authentication requires a guardian_token parameter to be provided which is the JWT. If this is present, Guardian.Phoenix.Socket will authenticate the connection and carry on or return an :error and not allow the connection.

On the javascript side provide your token when you connect.

let socket = new Socket("/ws");
socket.connect({guardian_token: jwt});

This works fine when all connections should be authenticated. In the case where you want some of them to be, you can manually sign in.

defmodule MyApp.UsersSocket do
  use Phoenix.Socket
  import Guardian.Phoenix.Socket

  def connect(%{"guardian_token" => jwt} = params, socket) do
    case sign_in(socket, jwt) do
      {:ok, authed_socket, guardian_params} ->
        {:ok, authed_socket}
      _ ->
        #unauthenticated socket
        {:ok, socket}
    end
  end

  def connect(_params, socket) do
    # handle unauthenticated connection
  end
end

Once you have an authenticated socket you can get the information from it:

claims = Guardian.Phoenix.Socket.current_claims(socket)
jwt = Guardian.Phoenix.Socket.current_token(socket)
user = Guardian.Phoenix.Socket.current_resource(socket)

If you need even more control, you can use the helpers provided by Phoenix.Guardian.Socket inside your Channel.

Phoenix Channels

We can use the Guardian.Phoenix.Socket module to help authenticate channels.

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

  def join(_room, %{"guardian_token" => token}, socket) do
    case sign_in(socket, token) do
      {:ok, authed_socket, _guardian_params} ->
        {:ok, %{message: "Joined"}, authed_socket}
      {:error, reason} ->
        # handle error
    end
  end

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

  def handle_in("ping", _payload, socket) do
    user = 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.

TODO

  • [x] Flexible serialization
  • [x] Integration with Plug
  • [x] Basic integrations like raw TCP
  • [x] Service2Service credentials. That is, pass the authentication results through many downstream requests.
  • [x] Integration with Phoenix channels
  • [x] Integrated permission sets
  • [x] Hooks into the authentication cycle
  • [x] Revoke tokens
  • [x] Refresh tokens