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Use Google, Github, Twitter, Facebook, or add your custom strategy for authorization to your Pow enabled Phoenix app.

Features

Installation

Add PowAssent to your list of dependencies in mix.exs:

defp deps do
  [
    # ...
    {:pow_assent, "~> 0.4.18"},

    # Optional, but recommended for SSL validation with :httpc adapter
    {:certifi, "~> 2.4"},
    {:ssl_verify_fun, "~> 1.1"},
    # ...
  ]
end

Run mix deps.get to install it.

Getting started

Set up Pow

It's required to set up Pow first. You can run these quick setup instructions if Pow hasn't already been set up.

If your user schema uses binary id, then run the PowAssent mix task(s) with the --binary-id flag.

Set up PowAssent

Install the necessary files:

mix pow_assent.install

This will add the following files to your app:

LIB_PATH/user_identities/user_identity.ex
PRIV_PATH/repo/migrations/TIMESTAMP_create_user_identities.ex

And also update the following files:

CONTEXT_PATH/users/user.ex
WEB_PATH/router.ex

Run migrations with mix setup. The following routes will be available in your app:

GET     /auth/:provider/new                    PowAssent.Phoenix.AuthorizationController :new
DELETE  /auth/:provider                        PowAssent.Phoenix.AuthorizationController :delete
GET     /auth/:provider/callback               PowAssent.Phoenix.AuthorizationController :callback
GET     /auth/:provider/add-user-id            PowAssent.Phoenix.RegistrationController :add_user_id
POST    /auth/:provider/create                 PowAssent.Phoenix.RegistrationController :create

Modified Pow templates

If you're modifying the Pow templates, then you have to generate the PowAssent template too:

mix pow_assent.phoenix.gen.templates

Otherwise, Pow will raise an error about missing template when the user id field template is shown.

You can use helpers from PowAssent.Phoenix.HTML.CoreComponents to render provider links:

# Minimal
<PowAssent.Phoenix.HTML.CoreComponents.provider_links conn={@conn} />

# With styling
<div class="space-y-4 bg-white mt-10">
  <PowAssent.Phoenix.HTML.CoreComponents.provider_links conn={@conn}>
    <:authorization_link :let={provider} class="block rounded-lg bg-zinc-600 hover:bg-zinc-700 py-2 px-3 text-sm font-semibold leading-6 text-white w-full text-center">
      <%= Phoenix.Naming.humanize(provider) %> <span aria-hidden="true">→</span>
    </:authorization_link>
  </PowAssent.Phoenix.HTML.CoreComponents.provider_links>
</div>

This can be used in the WEB_PATH/controllers/pow/session_html/new.html.heex, WEB_PATH/controllers/pow/registration_html/new.html.heex and WEB_PATH/controllers/pow/registration_html/edit.html.heex templates. You may want to import or alias the module in your web module.

By default "Sign in with PROVIDER" link is shown. A "Remove PROVIDER authentication" link will be shown instead if the user is signed in and the user already is authorized with the provider.

You can also use <.authorization_link conn={@conn} provider={provider} /> and <.deauthorization_link conn={@conn} provider={provider} /> to generate a link for a single provider.

Setting up a provider

Assent provides many strategies that you can use. Let's go through how to set up the Github strategy.

First, register a new app on Github and add http://localhost:4000/auth/github/callback as the callback URL. Then add the following to config/config.exs and add the client id and client secret (for production keys you would want to set this in config/prod.secret.exs):

config :my_app, :pow_assent,
  providers: [
    github: [
      client_id: "REPLACE_WITH_CLIENT_ID",
      client_secret: "REPLACE_WITH_CLIENT_SECRET",
      strategy: Assent.Strategy.Github
    ]
  ]

Now start (or restart) your Phoenix app, and visit http://localhost:4000/auth/github/new.

Nonce

For OIDC requests a nonce may be required. PowAssent can automatically generate the nonce if you pass nonce: true in the PowAssent configuration:

config :my_app, :pow_assent,
  providers: [
    example: [
      client_id: "REPLACE_WITH_CLIENT_ID",
      base_url: "https://server.example.com",
      authorization_params: [scope: "user:read user:write"],
      nonce: true,
      strategy: Assent.Strategy.OIDC
    ]
  ]

Custom provider

You can add your own custom strategy. See "Custom Provider" section of Assent readme for more.

I18n

The template can be generated and modified to use your Gettext module with mix pow_assent.phoenix.gen.templates

For flash messages, you should add them to your Pow.Phoenix.Messages module the same way as all Pow extension flash messages:

defmodule MyAppWeb.Pow.Messages do
  use Pow.Phoenix.Messages
  use Pow.Extension.Phoenix.Messages,
    extensions: [PowAssent]

  import MyAppWeb.Gettext

  # ...

  def pow_assent_signed_in(conn) do
    provider = Phoenix.Naming.humanize(conn.params["provider"])

    gettext("You've been signed in with %{provider}.", provider)
  end
end

Add messages_backend: MyAppWeb.Pow.Messages to your Pow configuration. You can find all messages in PowAssent.Phoenix.Messages.

Populate fields

To populate fields in your user struct that are fetched from the provider, you can override the user_identity_changeset/4 method to cast them:

defmodule MyApp.Users.User do
  use Ecto.Schema
  use Pow.Ecto.Schema
  use PowAssent.Ecto.Schema

  schema "users" do
    field :custom_field, :string

    pow_user_fields()

    timestamps()
  end

  def user_identity_changeset(user_or_changeset, user_identity, attrs, user_id_attrs) do
    user_or_changeset
    |> Ecto.Changeset.cast(attrs, [:custom_field])
    |> pow_assent_user_identity_changeset(user_identity, attrs, user_id_attrs)
  end
end

The fields available can be found in the normalize/2 method of the strategy module.

Disable registration

You can disable registration by using pow_assent_authorization_routes/0 instead of pow_assent_routes/0 in router.ex:

defmodule MyAppWeb.Router do
  use MyAppWeb, :router
  use Pow.Phoenix.Router
  use PowAssent.Phoenix.Router

  # ...

  pipeline :skip_csrf_protection do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :put_secure_browser_headers
  end

  # ...

  scope "/" do
    pipe_through :skip_csrf_protection

    pow_assent_authorization_post_callback_routes()
  end

  scope "/" do
    pipe_through :browser

    pow_routes()
    pow_assent_authorization_routes()
  end

  # ...
end

PowAssent will pick it up in the authorization flow, and prevent creating a user if the registration path is missing.

Cookie options are passed on to Plug.Conn.html.put_resp_cookie/4 and can be set by using the :auth_session_cookie_opts setting (and :reauthorization_cookie_opts for the PowAssent.Plug.Reauthorization plug):

config :my_app, :pow_assent,
    auth_session_cookie_opts: [
      secure: true,
      extra: "SameSite=Strict"
    ]

    # If you are using the reathorization plug:
    # reauthorization_cookie_opts: [
    #   secure: true
    # ]
  ]
]

HTTP Adapter

By default Erlangs built-in :httpc is used for requests. SSL verification is automatically enabled when :certifi and :ssl_verify_fun packages are available. :httpc only supports HTTP/1.1.

If you would like HTTP/2 support, you should consider adding Mint to your project.

Update mix.exs:

defp deps do
  [
    # ...
    {:mint, "~> 1.0"},
    {:castore, "~> 0.1.0"}, # Required for SSL validation
    # ...
  ]
end

Update the PowAssent configuration with:

config :my_app, :pow_assent,
  http_adapter: Assent.HTTPAdapter.Mint

Different module naming

PowAssent works by the assumption that you name your schema modules in the form of [App].[Context].[Schema]. If you have a different module naming, all you have to do is to add the has_many association to your user module like so:

defmodule MyApp.Lib.User do
  use Ecto.Schema
  use Pow.Ecto.Schema
  use PowAssent.Ecto.Schema

  schema "users" do
    has_many :user_identities,
      MyApp.Lib.UserIdentity,
      on_delete: :delete_all,
      foreign_key: :user_id

    pow_user_fields()

    # ...

    timestamps()
  end

  # ..
end

Otherwise you'll get an error that reads:

warning: invalid association `user_identities` in schema MyApp.Lib.User: associated schema MyApp.UserIdentities.UserIdentity does not exist

Callback URL with HTTPS behind proxy

PowAssent uses the Phoenix URL generator to generate the callback URL used in OAuth and OIDC flows. If you run your Phoenix app behind a proxy, then you should ensure that HTTPS endpoints are generated:

config :my_app, MyAppWeb.Endpoint,
  # ..,
  url: [scheme: "https", host: "example.com", port: 443]

Pow Extensions

PowEmailConfirmation

The e-mail fetched from the provider params is assumed confirmed if an email_verified key with value true also exists in the params. In that case the user will have :email_confirmed_at set. If email_verified isn't true in the provider params, or the user provides the e-mail, then the user will have to confirm their e-mail before they can sign in.

To prevent user enumeration attacks whenever there is a unique constraint error for e-mail the user will see confirmation required error message. However if email_verified is true in the provider params they will be see the form with changeset error. The same happens if pow_prevent_information_leak: false is set in conn.private.

PowInvitation

PowAssent works out of the box with PowInvitation.

Provider links will have an invitation_token query param if an invited user exists in the connection. This will be used in the authorization callback flow to load the invited user. If a user identity is created, the invited user will have the :invitation_accepted_at set.

PowPersistentSession

PowAssent doesn't support PowPersistentSession, as it's recommended to let the provider handle persistent session. PowAssent.Plug.Reauthorization can be used for this purpose.

You can enable the reauthorization plug in your WEB_PATH/router.ex by adding it to a pipeline:

defmodule MyAppWeb.Router do
  use MyAppWeb, :router
  # ...

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers
    plug PowAssent.Plug.Reauthorization,
      handler: PowAssent.Phoenix.ReauthorizationPlugHandler
  end

  # ...
end

You can also enable PowPersistentSession by using the PowAssent.Plug.put_create_session_callback/2 method:

defmodule MyAppWeb.Router do
  use MyAppWeb, :router
  # ...

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers
    plug :pow_assent_persistent_session
  end

  defp pow_assent_persistent_session(conn, _opts) do
    PowAssent.Plug.put_create_session_callback(conn, fn conn, _provider, _config ->
      PowPersistentSession.Plug.create(conn, Pow.Plug.current_user(conn))
    end)
  end

  # ...

Security concerns

All sessions created through PowAssent provider authentication are temporary. However, it's a good idea to do some housekeeping in your app and make sure that you have the level of security as warranted by the scope of your app. That may include requiring users to re-authenticate before viewing or editing their user details.

LICENSE

(The MIT License)

Copyright (c) 2018-2019 Dan Schultzer & the Contributors

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.