Support for uncommon HTTP Status codes and how to set custom headers?

Hi, we have a resource that takes a while to create and want to return `HTTP 202`, and in general want to follow the conventions laid out here: [https://farazdagi.com/posts/2014-10-16-rest-long-running-jobs/](https://farazdagi.com/posts/2014-10-16-rest-long-running-jobs/).
See here for a discussion of HTTP and long running processes: [https://softwareengineering.stackexchange.com/questions/316208/http-status-code-for-still-processing](https://softwareengineering.stackexchange.com/questions/316208/http-status-code-for-still-processing).