omniauth_callbacks_controller.rb

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def facebook
    @user = User.find_for_facebook_oauth(request.env["omniauth.auth"], current_user)

    if @user.persisted?
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success", :kind => "Facebook"
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.facebook_data"] = request.env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end
end

routes.rb

namespace "api" do
  resources :notebooks do
    resources :lessons
  end
end  



## Facebook auth (via omniauth)
devise_for :users, :controllers => { :omniauth_callbacks => "users/omniauth_callbacks" }
## API auth
devise_for :users, :controllers => {:sessions => 'api/sessions'}, :skip => [:sessions] do
  match 'api/login' => 'api/sessions#create', :via => [:get, :post]
  get 'api/logout' => 'api/sessions#destroy', :as => :destroy_user_session
end
# Devise auth
devise_for :users

sessions_controller.rb

class Api::SessionsController < Devise::SessionsController
  include Devise::Controllers::InternalHelpers

  before_filter :authenticate_user!, :except => [:create, :destroy]
  before_filter :ensure_params_exist
  respond_to :json

  def create
    user = warden.authenticate(:scope => :user)
    if user
      user.reset_authentication_token!
      render :json => {:access_token => user.authentication_token, :token_type => "persistant", :name => user.name}, :callback => params[:callback]
    else
      render :json => {:error => "invalid_grant"}, :callback => params[:callback]
    end
  end

  def destroy
    resource = User.find_for_database_authentication(:email => params[:user_login][:email])
    resource.authentication_token = nil
    resource.save
    render :json=> {:success=>true}
  end

  protected
  def ensure_params_exist
    return unless params[:user].blank?
    render :json=>{:success=>false, :message=>"missing user_login parameter"}, :status=>422
  end

  def invalid_login_attempt
    render :json=> {:success=>false, :message=>"Error with your login or password"}, :status=>401
  end
end