Fix broken callback_url from parent gem

omniauth/omniauth-oauth2#93 (comment)

The URL was being created incorrectly. This strips all the gunk that
Nest was complaining about.

[Fixes #151421294]

lib/omniauth/strategies/nest.rb

@@ -38,6 +38,12 @@ def callback_phase # rubocop:disable AbcSize, CyclomaticComplexity, MethodLength
         session["omniauth.expected_state"] = session["omniauth.state"]
         super
       end
+
+      # https://github.com/intridea/omniauth-oauth2/issues/93#issuecomment-257319242
+      # A bad merge broke most of the oauth2 gems for omniauth
+      def callback_url
+        full_host + script_name + callback_path
+      end
     end
   end
 end