Adds a test dependency on
[mock-oauth2-server](https://github.com/navikt/mock-oauth2-server/) for
integration tests for OAuth layer. Also includes fixes for some
regressions that were caught by the integration tests.
Reviewers: Manikumar Reddy <manikumar@confluent.io>, Lianet Magrans
<lmagrans@confluent.io>
Kirk True