Controller for authentication of Yammer API with OAuth2

application_controller.rb

class ApplicationController < ActionController::Base
  protect_from_forgery

  def user
    session[:current_user]
  end 

  def logined?
    not session[:current_user].nil?
  end 

  def oauth2_client
    @client ||= OAuth2::Client.new(ENV['CLIENT_ID'], ENV['CLIENT_SECRET'],
                  :site => 'https://www.yammer.com',
                  :authorize_url => '/dialog/oauth',
                  :token_url     => '/oauth2/access_token.json',
                  :mode          => :query,
                  :token_method  => :get)
  end 
end

auth_controller.rb

class AuthController < ApplicationController
  def login
    return if logined?
    return redirect_to oauth2_client.auth_code.authorize_url(:redirect_uri => callback_url)
  end 

  def logout
    session[:current_user] = nil 
    redirect_to welcome_path
  end 

  def callback
    token = oauth2_client.auth_code.get_token(params[:code])
    session[:current_user] = token['user']['id']
    access_token = eval(token.token)['token']
    token = OAuth2::AccessToken.new(token.client, access_token)

    token.post "api/v1/messages.json", :body => { :body => "This is test." }

    redirect_to welcome_path
  end 
end

routes.rb

YammerApp::Application.routes.draw do
  root :to => "welcome#index", :as => :welcome

  get 'login' => "auth#login", :as => :login
  get 'logout' => "auth#logout", :as => :logout
  get 'callback' => "auth#callback", :as => :callback
end