¿Cómo apoyar a los archivos virtuales en un sitio web C # MVC

Gracias a AaronLS, que comenzó a buscar cómo hacer un controlador personalizado que coger todas las solicitudes. Lástima que no era tan fácil de encontrar.

En primer lugar, es necesario informar a IIS que desea gestionar todos los archivos mediante la actualización del web.config:

<system.webServer>
    <httpErrors existingResponse="PassThrough" />
    <modules runAllManagedModulesForAllRequests="true">
        <remove name="FormsAuthentication"/>
    </modules>
</system.webServer>

(No sé que la httpErrors existingResponse = "PassThrough" realmente se necesita, podría haber sido un poco de solución anterior traté)

Luego que necesitaba para hacer mi propio controlador personalizado y configurarlo en el routeconfig:

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        // So my users can still login
        routes.MapRoute(
            name: "Account",
            url: "Account/{action}/{id}",
            defaults: new { controller = "Account", action = "Index", id = UrlParameter.Optional }
        );

        // For the upload controller to work
        routes.MapRoute(
            name: "Upload",
            url: "Upload/{action}/{id}",
            defaults: new { controller = "Upload", action = "Index", id = UrlParameter.Optional }
        );

        // And finally registrating my custom handler
        routes.Add(new Route("{*path}", new CustomRouteHandler()));

        // This was the original routeconfig
        //routes.MapRoute(
        //    name: "Default",
        //    url: "{controller}/{action}/{id}",
        //    defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        //);
    }
}
public class CustomRouteHandler : IRouteHandler
{
    public IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        return new CustomHttpHandler();
    }
}
public class CustomHttpHandler : IHttpHandler
{
    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
    public void ProcessRequest(HttpContext context)
    {
        // Get the subdomain requested
        var subdomain = context.Request.Url.Authority.Split(new char[] { '.', ':' }).FirstOrDefault();

        // Get the directory info about the requested subdomain
        DirectoryInfo info = new DirectoryInfo(context.Server.MapPath("~/Websites/" + subdomain));

        // Check if subdomain is not empty and exists
        if (!string.IsNullOrEmpty(subdomain) && info.Exists)
        {
            // Get the requested filename
            var filename = context.Request.Url.PathAndQuery.Split(new char[] { '?' }).FirstOrDefault();

            // If the root is requested change to index.html
            if (filename == "/") filename = "/index.html";

            // Translate requested filename to server path
            var fullname = context.Server.MapPath("~/Websites/" + subdomain + filename);

            // Respond the file
            ResponseFile(context, fullname);
        }
        else
        {
            // Subdomain not found so end the request
            context.Response.End();
        }
    }
    public void ResponseFile(HttpContext context, string fullname)
    {
        // Clear the response buffer
        context.Response.Clear();

        System.IO.Stream oStream = null;

        try
        {
            // Open the file
            oStream =
                new System.IO.FileStream
                    (path: fullname,
                    mode: System.IO.FileMode.Open,
                    share: System.IO.FileShare.Read,
                    access: System.IO.FileAccess.Read);

            // **************************************************
            context.Response.Buffer = false;

            // Setting the ContentType
            context.Response.ContentType = MimeMapping.GetMimeMapping(fullname);

            // Get the length of the file 
            long lngFileLength = oStream.Length;

            // Notify user (client) the total file length
            context.Response.AddHeader("Content-Length", lngFileLength.ToString());
            // **************************************************

            // Total bytes that should be read
            long lngDataToRead = lngFileLength;

            // Read the bytes of file
            while (lngDataToRead > 0)
            {
                // Verify that the client is connected or not?
                if (context.Response.IsClientConnected)
                {
                    // 8KB
                    int intBufferSize = 8 * 1024;

                    // Create buffer for reading [intBufferSize] bytes from file
                    byte[] bytBuffers =
                        new System.Byte[intBufferSize];

                    // Read the data and put it in the buffer.
                    int intTheBytesThatReallyHasBeenReadFromTheStream =
                        oStream.Read(buffer: bytBuffers, offset: 0, count: intBufferSize);

                    // Write the data from buffer to the current output stream.
                    context.Response.OutputStream.Write
                        (buffer: bytBuffers, offset: 0,
                        count: intTheBytesThatReallyHasBeenReadFromTheStream);

                    // Flush (Send) the data to output
                    // (Don't buffer in server's RAM!)
                    context.Response.Flush();

                    lngDataToRead =
                        lngDataToRead - intTheBytesThatReallyHasBeenReadFromTheStream;
                }
                else
                {
                    // Prevent infinite loop if user disconnected!
                    lngDataToRead = -1;
                }
            }
        }
        catch (Exception e)
        {
        }
        finally
        {
            if (oStream != null)
            {
                //Close the file.
                oStream.Close();
                oStream.Dispose();
                oStream = null;
            }
            context.Response.Close();
            context.Response.End();
        }
    }
}