Why is my omniauth-github not working with devise? - ruby-on-rails

Question

I have a rails app and I want to make a Github connect. I have followed the devise tutorial about Facebook and adapted it for Github.
I have this error on the callback, when accessing /users/auth/github/callback?code=xxxxxxx
ActionController::RoutingError (uninitialized constant Users):
I know that other posts are related to this issue but their answer do not fix my problem.
routes.rb
devise_for :users, :controllers => { :omniauth_callbacks => "users/omniauth_callbacks" }
app/controllers/users/omniauth_callbacks_controller.rb
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
def github
# You need to implement the method below in your model (e.g. app/models/user.rb)
#user = User.from_omniauth(request.env["omniauth.auth"])
if #user.persisted?
sign_in_and_redirect #user, :event => :authentication #this will throw if #user is not activated
set_flash_message(:notice, :success, :kind => "Github") if is_navigational_format?
else
session["devise.github_data"] = request.env["omniauth.auth"]
redirect_to new_user_registration_url
end
end
def failure
redirect_to root_path
end
end
models/user.rb
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable,
:omniauthable, :omniauth_providers => [:github]
def self.from_omniauth(auth)
where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
user.email = auth.info.email
user.password = Devise.friendly_token[0,20]
end
end
def self.new_with_session(params, session)
super.tap do |user|
if data = session["devise.github_data"] && session["devise.github_data"]["extra"]["raw_info"]
user.email = data["email"] if user.email.blank?
end
end
end
end