Spree engines mounted at locations other than the root "/" url, Omniauth middleware intercepts the wrong URL

My routes file:

mount Spree::Core::Engine, :at => '/store'

URL generated from app/views/shared/_social.html.erb:7 when calling spree.spree_user_omniauth_authorize_url(provider: method.provider) is correct. However, it makes its way past the Omniauth middleware which is looking for /auth/:provider instead of /store/auth/provider which fails when it gets to the  Spree::OmniauthCallbacksController's passthru action.

This pull request reconfigures Omniauth when the application starts to change the request_path to look for the correct route instead of the default /auth/:provider.