application_controller.rb

# app/controllers/application_controller.rb

# This application controller was extracted from a Rails-API application,
# the only line related to token authentication is the concern inclusion.
#
# The same line can be added to a regular Rails controller (which inherits from ActionController::Base).
#
# See https://github.com/rails-api/rails-api for details about Rails-API.

class ApplicationController < ActionController::API
  include ActionController::MimeResponds
  include ActionController::ImplicitRender

  # Concerns
  include TokenAuthentication

  respond_to :html, :xml, :json
end

# Example:
#
# class ApplicationController < ActionController::Base
#
#   # Concerns
#   include TokenAuthentication
#
#   respond_to :html, :xml, :json
# end

token_authenticable.rb

# app/models/concerns/token_authenticable.rb

module TokenAuthenticable
  extend ActiveSupport::Concern

  # Please see https://gist.github.com/josevalim/fb706b1e933ef01e4fb6
  # before editing this file, the discussion is very interesting.

  included do
    private :generate_authentication_token

    before_save :ensure_authentication_token
  end

  def ensure_authentication_token
    if authentication_token.blank?
      self.authentication_token = generate_authentication_token
    end
  end

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

  module ClassMethods
    # nop
  end
end

token_authentication.rb

# app/controllers/concerns/token_authentication.rb

module TokenAuthentication
  extend ActiveSupport::Concern

  # Please see https://gist.github.com/josevalim/fb706b1e933ef01e4fb6
  # before editing this file, the discussion is very interesting.

  included do
    private :authenticate_user_from_token!
    # This is our new function that comes before Devise's one
    before_filter :authenticate_user_from_token!
    # This is Devise's authentication
    before_filter :authenticate_user!
  end

  # For this example, we are simply using token authentication
  # via parameters. However, anyone could use Rails's token
  # authentication features to get the token from a header.
  def authenticate_user_from_token!
    user_email = params[:user_email].presence
    user = user_email && User.find_by(email: user_email)

    # Notice how we use Devise.secure_compare to compare the token
    # in the database with the token given in the params, mitigating
    # timing attacks.
    if user && Devise.secure_compare(user.authentication_token, params[:user_token])
      # Notice we are passing store false, so the user is not
      # actually stored in the session and a token is needed
      # for every request. If you want the token to work as a
      # sign in token, you can simply remove store: false.
      sign_in user, store: false
    end
  end

  module ClassMethods
    # nop
  end
end

user.rb

# app/models/user.rb

class User < ActiveRecord::Base

  # Concerns
  include TokenAuthenticable

  # Use any Devise module you want!

  # Include some (non-default) devise modules. Others available are:
  # :database_authenticatable, :registerable,
  # :recoverable, :rememberable, :trackable, :validatable
  # :confirmable, :lockable and :timeoutable
  devise :omniauthable, :omniauth_providers => [:open_id]

end

user_spec.rb

# spec/models/user_spec.rb

require 'spec_helper'

describe User do

  # attributes

  # ...
  it { expect(subject).to respond_to :authentication_token } # Token authentication

  # methods

  # ...

  describe "#ensure_authentication_token" do # Token authentication
    context "when the user has no authentication token" do

      subject(:user_created_without_auth_token) { FactoryGirl.create(:user) }

      it "creates one" do
        expect(subject.authentication_token).not_to be_blank
      end
    end
  end

end

XXXXXXXXXXXXX_add_authentication_token_to_users.rb

# db/migrate/XXXXXXXXXXXXX_add_authentication_token_to_users.rb

class AddAuthenticationTokenToUsers < ActiveRecord::Migration
  def change
    add_column :users, :authentication_token, :string

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