ExOauth2Provider

The no-brainer library to use for adding OAuth 2.0 provider capabilities to your Elixir app. You can use phoenix_oauth2_provider for easy integration with your Phoenix app.

Installation

Add ExOauth2Provider to your list of dependencies in mix.exs:

def deps do
  [
    # ...
    {:ex_oauth2_provider, "~> 0.5.6"}
    # ...
  ]
end

Run mix deps.get to install it.

Getting started

Generate the migrations and schema modules:

mix ex_oauth2_provider.install

Add the following to config/config.ex:

config :my_app, ExOauth2Provider,
  repo: MyApp.Repo,
  resource_owner: MyApp.Users.User

If you don't have any user setup, you shuld consider setting up Pow first.

Authorize code flow

Authorization request

You have to ensure that a resource_owner has been authenticated on the following endpoints, and pass the struct as the first argument in the following methods.

# GET /oauth/authorize?response_type=code&client_id=CLIENT_ID&redirect_uri=CALLBACK_URL&scope=read
case ExOauth2Provider.Authorization.preauthorize(resource_owner, params, otp_app: :my_app) do
  {:ok, client, scopes}             -> # render authorization page
  {:redirect, redirect_uri}         -> # redirect to external redirect_uri
  {:native_redirect, %{code: code}} -> # redirect to local :show endpoint
  {:error, error, http_status}      -> # render error page
end

# POST /oauth/authorize?response_type=code&client_id=CLIENT_ID&redirect_uri=CALLBACK_URL&scope=read
ExOauth2Provider.Authorization.authorize(resource_owner, params, otp_app: :my_app) do
  {:redirect, redirect_uri}         -> # redirect to external redirect_uri
  {:native_redirect, %{code: code}} -> # redirect to local :show endpoint
  {:error, error, http_status}      -> # render error page
end

# DELETE /oauth/authorize?response_type=code&client_id=CLIENT_ID&redirect_uri=CALLBACK_URL&scope=read
ExOauth2Provider.Authorization.deny(resource_owner, params, otp_app: :my_app) do
  {:redirect, redirect_uri}         -> # redirect to external redirect_uri
  {:error, error, http_status}      -> # render error page
end

Authorization code grant

# POST /oauth/token?client_id=CLIENT_ID&client_secret=CLIENT_SECRET&grant_type=authorization_code&code=AUTHORIZATION_CODE&redirect_uri=CALLBACK_URL
case ExOauth2Provider.Token.grant(params, otp_app: :my_app) do
  {:ok, access_token}               -> # JSON response
  {:error, error, http_status}      -> # JSON response
end

Revocation

# GET /oauth/revoke?client_id=CLIENT_ID&client_secret=CLIENT_SECRET&token=ACCESS_TOKEN
case ExOauth2Provider.Token.revoke(params, otp_app: :my_app) do
  {:ok, %{}}                        -> # JSON response
  {:error, error, http_status}      -> # JSON response
end

Revocation will return {:ok, %{}} status even if the token is invalid.

Authorization code flow in a Single Page Application

ExOauth2Provider doesn't support implicit grant flow. Instead you should set up an application with no client secret, and use the Authorize code grant flow. client_secret isn't required unless it has been set for the application.

Other supported token grants

Client credentials

# POST /oauth/token?client_id=CLIENT_ID&client_secret=CLIENT_SECRET&grant_type=client_credentials
case ExOauth2Provider.Token.grant(params, otp_app: :my_app) do
  {:ok, access_token}               -> # JSON response
  {:error, error, http_status}      -> # JSON response
end

Refresh token

Refresh tokens can be enabled in the configuration:

config :my_app, ExOauth2Provider,
  repo: MyApp.Repo,
  resource_owner: MyApp.Users.User,
  use_refresh_token: true

The refresh_token grant flow will then be enabled.

# POST /oauth/token?client_id=CLIENT_ID&client_secret=CLIENT_SECRET&grant_type=refresh_token&refresh_token=REFRESH_TOKEN
case ExOauth2Provider.Token.grant(params, otp_app: :my_app) do
  {:ok, access_token}               -> # JSON response
  {:error, error, http_status}      -> # JSON response
end

Username and password

You'll need to provide an authorization method that accepts username and password as arguments, and returns {:ok, resource_owner} or {:error, reason}. Here'a an example:

# Configuration in config/config.exs
config :my_app, ExOauth2Provider,
  password_auth: {Auth, :authenticate}

# Module example
defmodule Auth do
  def authenticate(username, password, otp_app: :my_app) do
    User
    |> Repo.get_by(email: username)
    |> verify_password(password)
  end

  defp verify_password(nil, password) do
    check_pw("", password) # Prevent timing attack

    {:error, :no_user_found}
  end
  defp verify_password(%{password_hash: password_hash} = user, password) do
    case check_pw(password_hash, password) do
      true  -> {:ok, user}
      false -> {:error, :invalid_password}
    end
  end
end

The password grant flow will then be enabled.

# POST /oauth/token?client_id=CLIENT_ID&grant_type=password&username=USERNAME&password=PASSWORD
case ExOauth2Provider.Token.grant(params, otp_app: :my_app) do
  {:ok, access_token}               -> # JSON response
  {:error, error, http_status}      -> # JSON response
end

Scopes

Server wide scopes can be defined in the configuration:

config :my_app, ExOauth2Provider,
  repo: MyApp.Repo,
  resource_owner: MyApp.Users.User,
  default_scopes: ~w(public),
  optional_scopes: ~w(read update)

Plug API

ExOauth2Provider.Plug.VerifyHeader

Looks for a token in the Authorization Header. If one is not found, this does nothing. This will always be necessary to run to load access token and resource owner.

ExOauth2Provider.Plug.EnsureAuthenticated

Looks for a verified token loaded by VerifyHeader. If one is not found it will call the :unauthenticated method in the :handler module.

You can use a custom :handler as part of a pipeline, or inside a Phoenix controller like so:

defmodule MyAppWeb.MyController do
  use MyAppWeb, :controller

  plug ExOauth2Provider.Plug.EnsureAuthenticated,
    handler: MyAppWeb.MyAuthErrorHandler
end

The :handler module always defaults to ExOauth2Provider.Plug.ErrorHandler.

ExOauth2Provider.Plug.EnsureScopes

Looks for a previously verified token. If one is found, confirms that all listed scopes are present in the token. If not, the :unauthorized function is called on your :handler.

defmodule MyAppWeb.MyController do
  use MyAppWeb, :controller

  plug ExOauth2Provider.Plug.EnsureScopes,
    handler: MyAppWeb.MyAuthErrorHandler, scopes: ~w(read write)
end

When scopes' sets are specified through a :one_of map, the token is searched for at least one matching scopes set to allow the request. The first set that matches will allow the request. If no set matches, the :unauthorized function is called.

defmodule MyAppWeb.MyController do
  use MyAppWeb, :controller

  plug ExOauth2Provider.Plug.EnsureScopes,
    handler: MyAppWeb.MyAuthErrorHandler,
    one_of: [~w(admin), ~w(read write)]
end

Current resource owner and access token

If the Authorization Header was verified, you'll be able to retrieve the current resource owner or access token.

ExOauth2Provider.Plug.current_access_token(conn) # access the token in the default location
ExOauth2Provider.Plug.current_access_token(conn, :secret) # access the token in the secret location

ExOauth2Provider.Plug.current_resource_owner(conn) # Access the loaded resource owner in the default location
ExOauth2Provider.Plug.current_resource_owner(conn, :secret) # Access the loaded resource owner in the secret location

Custom access token generator

You can add your own access token generator, as this example shows:

# config/config.exs
config :my_app, ExOauth2Provider,
  access_token_generator: {AccessToken, :new}

defmodule AccessToken
  def new(access_token) do
    with_signer(%JWT.token{
      resource_owner_id: access_token.resource_owner_id,
      application_id: access_token.application.id,
      scopes: access_token.scopes,
      expires_in: access_token.expires_in,
      created_at: access_token.created_at
    }, hs256("my_secret"))
  end
end

Remember to change the field type for the token column in the oauth_access_tokens table to accepts tokens larger than 255 characters.

Custom access token response body

You can add extra values to the response body.

# config/config.exs
config :my_app, ExOauth2Provider,
  access_token_response_body_handler: {CustomResponse, :response}

defmodule CustomResponse
  def response(response_body, access_token) do
    Map.merge(response_body, %{user_id: access_token.resource_owner.id})
  end
end

Remember to change the field type for the token column in the oauth_access_tokens table to accepts tokens larger than 255 characters.

Using binary id

Generate migration file with binary id

You'll need to create the migration file and schema modules with the argument --binary-id:

mix ex_oauth2_provider.install --binary-id

Acknowledgement

This library was made thanks to doorkeeper, guardian and authable, that gave the conceptual building blocks.

Thanks to Benjamin Schultzer for helping to refactor the code.

LICENSE

(The MIT License)

Copyright (c) 2017-2019 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.