UnityWebRequest doesn't support async/await operations natively. With this small extension, it now has an awaiter and can be cancelled via a CancellationToken

UnityWebRequestExtension.cs

using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using UnityEngine.Networking;

namespace UnityUtilities.Networking.Extensions
{
    public static class UnityWebRequestExtension
    {
        public static async Task<UnityWebRequest.Result> SendWebRequestAsync(this UnityWebRequest request, CancellationToken ct = default)
        {
            if (ct.CanBeCanceled)
            {
                ct.Register(request.Abort);
            }

            return await request.SendWebRequest();
        }

        private static TaskAwaiter<UnityWebRequest.Result> GetAwaiter(this UnityWebRequestAsyncOperation webRequestOperation)
        {
            TaskCompletionSource<UnityWebRequest.Result> tcs = new TaskCompletionSource<UnityWebRequest.Result>();

            webRequestOperation.completed += SetResult;

            void SetResult(UnityEngine.AsyncOperation _)
            {
                webRequestOperation.completed -= SetResult;
                tcs.TrySetResult(webRequestOperation.webRequest.result);
            }

            if (webRequestOperation.isDone) 
            {
                webRequestOperation.completed -= SetResult;
                tcs.TrySetResult(webRequestOperation.webRequest.result);
            }

            return tcs.Task.GetAwaiter();
        }
    }
}