If you have Ruby on Rails App and want to use a custom OmniAuth Callback URL (Something other than /auth), there is a configuration value that you can set.
/config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do provider :twitter, { :callback_path => "/myauth/shibboleth/callback" } end
Replace “myauth” with the path that you prefer to use. This will allow for a different callback URL when users aren’t logged in. Tested with Rails 4.2 and Ruby 2.2.