Refactor AuthSCH endpoint

We can use [JSON dumper](https://github.com/TheRusskiy/json_dumper) or [Active Model serializer](https://github.com/rails-api/active_model_serializers) to do this.

The issue names the AuthSCH endpoint but no file or test. Start by locating that endpoint and comparing the JSON dumper and Active Model serializer options named in the issue. The intended serializer and acceptance checks are not defined, so clarify those before implementation.

Written by the indexing model from the issue text.