Rails API Social Login

README.md

Rails API-Only Social Login

This is another piece of code I've extrapolated from a Ruby on Rails project I'm currently working on. The code implmenets social login with a RoR API-based application, targeted at API clients.

The setup does not involve any browser-redirects or sessions as you would have to use working with Omniauth. Instead, what it does is takes an access_token generated on client-side SDKs, retireves user info from the access token and creates a new user and Identity in the database.

This setup works with native applications as described in the Google iOS Sign In Docs (see Authenticating with a backend server) A quote from that page pretty much sums up how this works:

After you have verified the token, check if the user is already in your user database. If so, establish an authenticated session for the user. If the user isn't yet in your user database, create a new user record from the information in the ID token payload, and establish a session for the user. You can prompt the user for any additional profile information you require when you detect a newly created user in your app.

The basic flow of the login is:

• You sign in using the respective native sdks on your mobile/js clients
• An access_token/id_token is retireved from the mobile SDKs
• A request is made to your Rails Application POST /identities/:provider with the token
• The server then fetches the user data from the token after validating it with the provider
• The server then creates a user profile & Identity based on that information.

In comparison, if you were using Omniauth you would have to:

• Open up a web view in your mobile app linking to your backend
• Your user is redirected from your backend to the external provider
• The user signs in with the external provider
• The user is redirected back to your backend
• The backend generates a user account
• Then it generates an auth token (assuming you're using JWT auth)
• The backend redirects the user back to the native app with the access token.

So there's an advantage to using this setup, it's a lot easier to work with a single JSON API endpoint than it is to work with a bunch of redirects in a web view.

However, if you are using a traditional Rails Application (not a rails api), you should totally go with Omniauth and save all the hastle.

The code is quite modular so it will be extemely easy to add support for another login provider if needed. It's a matter of creating another Provider::Base super class and including the provider name in your Identity.providers array.

Basic Structure

There are quite a lot of files in this, each with different roles.

base_provider.rb

An abstract class that serves as a base for all the different login providers making it easy to implement new providers if needed. Provides common extractions for methods.

facebook_provider.rb

A provider class for handling login with facebook.

Note: The fields requested must match those requested on the native side otherwise you're going to get a run-time error becuase the granted acccess token won't have adequate permissions

google_provider.rb

A provider class for handling login with google. You need to provide an array of client_ids for the different clients you will have needing to sign in e.g. iOS App, Android App, React App, Windows App etc.

In this example, I only have one (ios_client_id)

provider_credentials.rb

Just an object to handle the credentials (access token/refresh token)

provider_info.rb

This provides a common interface for the User Information retrieved from the external APIs. Similar to the Omniauth env['auth']

identity.rb

So each user has what I call an Identity which is just an external login. If you want your app to only support one external login e.g. facebook only, this identities table wouldn't be needed as you could just store the uid/provider/access_token on the user model.

The identities table is structured like so:

    create_table :identities do |t|
      t.belongs_to :user, null: false, foreign_key: true
      t.string :provider, null: false
      t.string :uid, null: false
      t.string :access_token
      t.string :refresh_token
      t.jsonb :auth_hash, default: {}

      t.timestamps
    end
    
    add_index :identities, %i[provider uid], unique: true

Dependencies

Right now, I've implemented only two providers - Google and Facebook auth. The dependencies that I'm using are

gem 'google-id-token', git: 'https://github.com/google/google-id-token.git'
gem 'koala'

Note: Make sure to install the google-id-token gem from the repo (as of 26th April 2020) in order to support passing an array of client_ids

Specs/Tests

The tests can be found here

base_provider.rb

module External
  # A base class for handling external logins
  module Provider
    class Base
      attr_reader :access_token, :refresh_token, :client

      def initialize(access_token, refresh_token = nil)
        handle_missing_access_token unless access_token.present?

        @access_token = access_token
        @refresh_token = refresh_token
        @client = retrieve_client
      end

      def self.for(provider)
        class_name = provider.to_s.classify
        "External::Provider::#{class_name}".safe_constantize
      end

      # The name of the provider
      def self.name
        :base
      end

      # The user's info
      def info
        handle_unimplmeneted_method
      end

      # The user's credentials
      def credentials
        ProviderCredentials.new do |c|
          c.access_token = access_token
          c.refresh_token = refresh_token
        end
      end

      # The raw info returned from the hash
      def raw_info
        @raw_info ||= retrieve_user_info.deep_symbolize_keys
      end

      # Returns the raw info hash from the client
      def retrieve_user_info
        handle_unimplmeneted_method
      end

      def retrieve_client
        handle_unimplmeneted_method
      end

      private

      def handle_missing_access_token
        raise Errors::Domain, status: 422, message: 'missing token'
      end

      def handle_unimplmeneted_method(method = :method)
        raise StandardError, "Expected super class to override #{method}"
      end
    end
  end
end

facebook_provider.rb

module External
  module Provider
    class Facebook < Base
      def info
        ProviderInfo.new do |i|
          i.provider = External::Provider::Facebook.name
          i.date_format = '%m/%d/%Y'
          i.uid = raw_info[:id]
          i.email = raw_info[:email]
          i.birthday = raw_info[:birthday]
          i.first_name = raw_info[:first_name]
          i.last_name = raw_info[:last_name]
          i.name = raw_info[:name]
        end
      end

      def retrieve_client
        Koala::Facebook::API.new access_token
      end

      def retrieve_user_info
        client.get_object(
          :me,
          fields: %w[id email birthday first_name last_name]
        )
      end

      def self.name
        :facebook
      end
    end
  end
end

google_provider.rb

module External
  module Provider
    class Google < Base
      def info
        ProviderInfo.new do |i|
          i.provider = External::Provider::Google.name
          i.avatar = raw_info[:picture]
          i.first_name = raw_info[:given_name]
          i.last_name = raw_info[:family_name]
          i.email = raw_info[:email]
          i.name = raw_info[:name]
          i.uid = raw_info[:sub]
        end
      end

      def retrieve_client
        GoogleIDToken::Validator.new
      end

      def retrieve_user_info
        client.check(
          id_token,
          client_ids
        )
      end

      def self.name
        :google
      end

      private

      # The different clients your app needs to authenticate agains
      # E.g. iOS, Android, Web etc.
      def client_ids
        [Rails.application.credentials.google[:ios_client_id]]
      end

      alias id_token access_token
    end
  end
end

identities_controller.rb

class Api::V1::IdentitiesController < ApplicationController
  before_action :authenticate_for_identity!
  attr_reader :provider, :identity, :user, :access_token, :refresh_token

  # POST /identities/:provider
  def provider_create
    @provider = params[:provider]

    # We want to make sure we support the provider
    if Identity.valid_provider?(provider)
      set_identity
      return unless set_user

      # If the identity exists, we want to update it
      if identity.present?
        identity.update identity_params

      # Create a new identity for this user
      else
        user.identities.create identity_params
      end

      # Finally we want to create a new auth token pair for the user
      issue_tokens

      # Render the user object and the auth tokens
      render_json data: {
        token: { access_token: access_token, refresh_token: refresh_token },
        user: UserBlueprint.render_as_json(user)
      }, status: :created
    else
      # Render an error saying the provider is not supported
      render_unsupported_provider_error
    end
  end

  def set_identity
    @identity = Identity.where(provider: provider, uid: external.info.uid).first
  end

  def set_user
    # The user is already logged in (access_token present in request)
    # We want to set the user to the current user
    if current_user.present?
      @user = current_user

    # The user has signed in with this provider before
    # Return the existing account
    elsif identity.present?
      @user = identity.user

    # There is an existing user account with the same email & the user is not
    # logged in. We don't want to create an account for safety.
    # Tell the user to sign in to their account and link it there
    elsif User.where(email: external.info.email).any?
      render_existing_account_error provider: provider
      return false
    # The user has never signed in before, we want to create a new account from
    # the external info object
    else
      @user = User.create_from_provider_info(external.info)
    end

    true
  end

  # We want to update the identity object with the new uid and provider.
  # Storing the ccess_token or refresh_token is optional since that
  # can be delt with on the native clients.
  def identity_params
    {
      provider: external.info.provider,
      uid: external.info.uid,
      access_token: external.credentials.access_token,
      refresh_token: external.credentials.refresh_token,
      auth_hash: external.info.to_h
    }
  end

  def issue_tokens
    @access_token, @refresh_token = Jwt::Issuer.call user
    response.set_header 'Access-token', access_token
    response.set_header 'Refresh-token', refresh_token
  end

  private

  # Returns the External::Provider object for the current provider
  # We can access the user info object and raw_info hash from here
  def external
    @external ||= External::Provider::Base
      .for(provider)
      .new(create_params[:token])
  end

  def create_params
    params.require(:data).permit(:token)
  end
end

identity.rb

class Identity < ApplicationRecord
  belongs_to :user

  PROVIDERS = %w[facebook google].freeze

  PROVIDERS.each do |provider|
    scope provider, -> { where(provider: provider) }
  end

  validates :uid, uniqueness: { scope: :provider }, presence: true
  validates :provider, inclusion: {
    in: PROVIDERS,
    message: 'this provider is not supported'
  }, presence: true

  def self.providers
    PROVIDERS
  end

  def self.valid_provider?(provider)
    providers.include?(provider.to_s)
  end
end

provider_credentials.rb

module External
  class ProviderCredentials
    attr_accessor :access_token, :refresh_token, :expires, :expires_at

    def initialize
      yield self if block_given?
    end

    def to_h
      {
        access_token: access_token,
        refresh_token: refresh_token,
        expires: expires,
        expires_at: expires_at
      }
    end

    alias hash to_h
  end
end

provider_info.rb

module External
  class ProviderInfo
    attr_accessor :uid, :email, :username, :date_format, :avatar, :provider
    attr_writer :birthday, :first_name, :last_name, :name

    def initialize
      yield self if block_given?
    end

    def first_name
      raw_name = @first_name

      if raw_name.present?
        raw_name
      elsif @name.present?
        split_name = @name.split(' ')
        if split_name.length > 1
          @name.split(' ')[0..-2].join(' ')
        else
          split_name.first
        end
      end
    end

    def last_name
      raw_name = @last_name

      if raw_name.present?
        raw_name
      elsif @name.present?
        split_name = @name.split(' ')
        return split_name if split_name.length > 1
      end
    end

    def birthday
      raw_value = @birthday

      if raw_value.is_a?(String)
        if date_format.present?
          Date.strptime raw_value, date_format
        else
          Date.parse raw_value
        end
      elsif raw_value.is_a?(Integer)
        Time.at(raw_value).to_date
      else
        raw_value
      end
    end

    def name
      raw_name = @name

      if raw_name.present?
        raw_name
      elsif @first_name.present? && @last_name.present?
        "#{@first_name} #{@last_name}"
      elsif @first_name.present?
        @first_name
      end
    end

    def to_h
      {
        uid: uid,
        email: email,
        username: username,
        birthday: birthday,
        first_name: first_name,
        last_name: last_name,
        name: name
      }
    end

    alias hash to_h
  end
end