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Multi-provider authentication for your Pow enabled app
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README.md

PowAssent

Build Status hex.pm

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, "~> 0.3.2"},

    # 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

Update LIB_PATH/users/user.ex:

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

  schema "users" do
    pow_user_fields()

    # ...

    timestamps()
  end

  # ..
end

Set up router.ex:

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

  # ...

  scope "/" do
    pipe_through [:browser]
    pow_routes()
    pow_assent_routes()
  end

  # ...
end

The following routes will now be available in your app:

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

Remember to run the new migrations with:

mix ecto.setup

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.

Provider links

You can use PowAssent.Phoenix.ViewHelpers.provider_links/1 to add provider links to your template files:

<%= for link <- PowAssent.Phoenix.ViewHelpers.provider_links(@conn),
  do: content_tag(:span, link) %>

This can be used in the WEB_PATH/templates/pow/session/new.html.eex, WEB_PATH/templates/pow/registration/new.html.eex and WEB_PATH/templates/pow/registration/edit.html.eex templates.

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 have authorized with the provider.

You can also call PowAssent.Phoenix.ViewHelpers.authorization_link/2 and PowAssent.Phoenix.ViewHelpers.deauthorization_link/2 to generate a link for a single provider.

Setting up a provider

PowAssent has multiple 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: PowAssent.Strategy.Github
    ]
  ]

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

Custom provider

You can add your own custom strategy.

Here's an example of an OAuth 2.0 implementation using PowAssent.Strategy.OAuth2.Base:

defmodule TestProvider do
  use PowAssent.Strategy.OAuth2.Base

  def default_config(_config) do
    [
      site: "http://localhost:4000/",
      authorize_url: "http://localhost:4000/oauth/authorize",
      token_url: "http://localhost:4000/oauth/access_token",
      user_url: "/user",
      authorization_params: [scope: "email profile"]
    ]
  end

  def normalize(_config, user) do
    %{
      "uid"   => user["sub"],
      "name"  => user["name"],
      "email" => user["email"]
    }
  end
end

You can also use PowAssent.Strategy:

defmodule TestProvider do
  @behaviour PowAssent.Strategy

  @spec authorize_url(Keyword.t()) :: {:ok, %{url: binary()}} | {:error, term()}
  def authorize_url(config) do
    # Generate authorization url
  end

  @spec callback(Keyword.t(), map()) :: {:ok, %{user: map()}} | {:error, term()}
  def callback(config, params) do
    # Handle callback response
  end
end

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 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.

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

  # ...

  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.

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, "~> 0.1.0"},
    {:castore, "~> 0.1.0"}, # Required for SSL validation
    # ...
  ]
end

Update the PowAssent configuration with:

config :my_app, :pow_assent,
  http_adapter: PowAssent.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

Pow Extensions

PowEmailConfirmation

The e-mail fetched from the provider is assumed already confirmed, and the user will have :email_confirmed_at set when inserted. If a user enters an e-mail then the user will have to confirm their e-mail before they can sign in.

PowInvitation

PowAssent works out of the box with PowInvitation. If a user identity is created, the an invited user will have the :invitation_accepted_at set.

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.

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.

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