Google authentification error "no route match"

I have a problem, I follow this tutorial :http://ift.tt/1Q9p04x

I have done everything exept rails g controller home show because i have already a static_pages controller and home.html.erb

So in my route.rb i have replace this line from tuto :

resource :home, only: [:show] root to: "home#show"

by

resource :static_pages, only: [:home] root to: 'static_pages#home'

but when i click on the link after i've launched the server (localhost) i have this error :

No route matches [GET] "/auth/google_oauth2"

Do you have any Idea about this problem ? Hope you could help me.

Thank you in advance.