CancelCancel.cs

using System;
using System.Threading;
using System.Threading.Tasks;

namespace Jedlix.Assets.Application.API
{
    public class Demo
    {
        public void Foo()
        {
            var cts = new CancellationTokenSource(TimeSpan.FromSeconds(1));

            var task = Task.Factory.StartNew(LongRunningApiCall, cts.Token);

            try
            {
                task.GetAwaiter().GetResult();
            }
            catch (TaskCanceledException)
            {
                // ignore or whatever
            }
        }

        private void LongRunningApiCall()
        {
            // Do something stupid here
        }
    }
}