Get "time of upload started" - asp.net-web-api

Question

I'm developing a WebAPI service in which you can upload a file. The Action looks something like this:
[HttpPost]
public async Task<IHttpActionResult> PostAsync(byte[] content)
{
var now = DateTime.UtcNow;
}
The client which are using the WebAPI also provides a timestamp as header which is used together with some HMAC-stuff to authenticate. One part of the auth check is to validate the timestamp. We parse the timestamp and checks if it is +/- 5 minutes from now. If not then the auth fails.
It works great for all our API calls except this upload API (in some cases). The problem is that sometimes a user uploads a large file over a slow connection and therefore it takes more than 5 minutes to upload the file and the point in time where we check is AFTER the whole file has been uploaded.
Therefore:
Can we somehow do the HMAC check BEFORE the whole file is uploaded? (the file itself (HTTP Content) is not used in the HMAC check). Today we are using an ActionFilter.
Can I get the "time of request" (first byte arrived or whatever) in my Action code?
Thanks!

Answer 1

So, after some investigation I came up with a much better solution:
Use a HTTP Module to do the actual HMAC authentication.
After reading this blog post (http://blogs.msdn.com/b/tmarq/archive/2007/08/30/iis-7-0-asp-net-pipelines-modules-handlers-and-preconditions.aspx) I got a much better understanding of how IIS Works.
I decided to use a HTTP Module which is invoked before the MVC Action.
The code ended up like this:
public class HmacModule : IHttpModule
{
public void Init(HttpApplication context)
{
EventHandlerTaskAsyncHelper taskAsyncHelper = new EventHandlerTaskAsyncHelper(Authenticate);
context.AddOnBeginRequestAsync(taskAsyncHelper.BeginEventHandler, taskAsyncHelper.EndEventHandler);
}
private async Task Authenticate(object sender, EventArgs e)
{
var context = ((HttpApplication)sender).Context;
var request = context.Request;
var authResponse = await CheckAuthentication(request);
if (!authResponse.HasAccess)
{
context.Response.StatusCode = (int)HttpStatusCode.Unauthorized;
context.Response.StatusDescription = authResponse.ErrorMessage;
if (authResponse.Details != null)
context.Response.Write(authResponse.Details);
context.Response.End();
}
}
}
I hope this helps others in the same situation...