Hi Thomas,

Here's a link to Microsoft's documentation on how Cancellation Tokens work. They can't be used as you describe, though. They're used to help with manual cancellation of threads by an owning thread. You cannot cancel an already ongoing operation on a REST API. If you have a long-running operation that should be cancelable, what you can do is create a job queue on the server to handle long-running operations and let the Web API and the Job Queue communicate with each other using message brokers. You would have to expose another set of endpoints for canceling the jobs, and the way to cancel these jobs is particular to the job queue's implementation.

This is a very good read on the topic: https://stackoverflow.com/questions/14710822/how-to-queue-background-tasks-in-asp-net-web-api

I hope this helps!

Regards,
Francisco