User Authentication with Grape and Devise

Question

I have difficulties to understand and also properly implement User Authentication in APIs. In other words, I have serious problem to understand the

Answer 1

Although I like the question and the answer given by @MZaragoza I think it is worth noting that token_authentical has been removed from Devise for a reason! Use of the tokens are vulnerable for timing attacks. See also this post and Devise's blog Therefor I haven't upvoted @MZaragoza's answer.

In case you use your API in combination with Doorkeeper, you could do something similar, but instead of checking for the authentication_token in the User table/model you look for the token in the OauthAccessTokens table, i.e.

def authenticated
   return true if warden.authenticated?
   params[:access_token] && @user = OauthAccessToken.find_by_token(params[:access_token]).user
end

This is more safe, because that token (i.e. the actual access_token) exists only for a certain amount of time.

Note in order to be able to do this you must have a User model and OauthAccessToken model, with:

class User < ActiveRecord::Base

   has_many :oauth_access_tokens

end

class OauthAccessToken < ActiveRecord::Base
    belongs_to :user, foreign_key: 'resource_owner_id'
end

EDIT: Please also note that generally you should not include the access_token in the URL: http://tools.ietf.org/html/draft-ietf-oauth-v2-bearer-16#section-2.3

Answer 2

Add token_authenticable to devise modules (works with devise versions <=3.2)

In user.rb add :token_authenticatable to the list of devise modules, it should look something like below:

class User < ActiveRecord::Base
# ..code..
  devise :database_authenticatable,
    :token_authenticatable,
    :invitable,
    :registerable,
    :recoverable,
    :rememberable,
    :trackable,
    :validatable

  attr_accessible :name, :email, :authentication_token

  before_save :ensure_authentication_token
# ..code..
end

Generate Authentication token on your own (If devise version > 3.2)

class User < ActiveRecord::Base
# ..code..
  devise :database_authenticatable,
    :invitable,
    :registerable,
    :recoverable,
    :rememberable,
    :trackable,
    :validatable

  attr_accessible :name, :email, :authentication_token

  before_save :ensure_authentication_token

  def ensure_authentication_token
    self.authentication_token ||= generate_authentication_token
  end

  private

  def generate_authentication_token
    loop do
      token = Devise.friendly_token
      break token unless User.where(authentication_token: token).first
    end
  end

Add migration for authentiction token

rails g migration add_auth_token_to_users
      invoke  active_record
      create    db/migrate/20141101204628_add_auth_token_to_users.rb

Edit migration file to add :authentication_token column to users

class AddAuthTokenToUsers < ActiveRecord::Migration
  def self.up
    change_table :users do |t|
      t.string :authentication_token
    end

    add_index  :users, :authentication_token, :unique => true
  end

  def self.down
    remove_column :users, :authentication_token
  end
end

Run migrations

rake db:migrate

Generate token for existing users

We need to call save on every instance of user that will ensure authentication token is present for each user.

User.all.each(&:save)

Secure Grape API using auth token

You need to add below code to the API::Root in-order to add token based authentication. If you are unware of API::Root then please read Building RESTful API using Grape

In below example, We are authenticating user based on two scenarios – If user is logged on to the web app then use the same session – If session is not available and auth token is passed then find user based on the token

# lib/api/root.rb
module API
  class Root < Grape::API
    prefix    'api'
    format    :json

    rescue_from :all, :backtrace => true
    error_formatter :json, API::ErrorFormatter

    before do
      error!("401 Unauthorized", 401) unless authenticated
    end

    helpers do
      def warden
        env['warden']
      end

      def authenticated
        return true if warden.authenticated?
        params[:access_token] && @user = User.find_by_authentication_token(params[:access_token])
      end

      def current_user
        warden.user || @user
      end
    end

    mount API::V1::Root
    mount API::V2::Root
  end
end