This question is related to my ASP.NET MVC 2 development, but it could apply to any MVC environment and a question of where the logic should go.

So let's say I have a controller that takes an online payment such as a shopping cart application. And I have the method that accepts the customers' credit card information:

public class CartController : Controller
    CartRepository cartRepository = new CartRepository()

    [HttpPost]
    public ActionResult Payment(PaymentViewModel rec)
    {
        if(!ModelState.IsValid)
        {
            return View(rec);
        }

        // process payment here

        return RedirectToAction("Receipt");
    }

At the comment process payment here should the payment processing be handled:

1. In the controller?
2. By the repository?
3. Someplace else?