Just in case I may need them later, I have attached ready-to-use feature just to drop into solution and adjust:
WebApi.zip (6.9KB)
Update: I have plaed ready-to-use code to GitHub, please consider cloning
this repo.
It is .NET 4.6.2 and has references to Sitecore 9.0 update 1 (rev. 9.0.171219)
ServicesClient
WebApi