Would appreciate if someone could advise on the steps needed to integrate a payment provider.  Specifically I'm looking to use the Authorize.Net one that comes as a plugin with Merchello.

I have a checkout process set up working fine with the "Cash" payment provider.

So given I have a basket set up with a saved billing address, shipping address and shipment quote, I then have provided my customer a choice of payment methods, one of which is credit card based on Authorize.Net which has been configured with the key details in the back-office.  Posting that form calls this code:

    var basket = GetBasket();
    if (basket.IsEmpty)
    {
        return RedirectToBasketPage();
    }

    if (ModelState.IsValid)
    {
        // Associate the payment method with the order
        var paymentMethod = MerchelloContext.Current.Gateways.Payment.GetPaymentGatewayMethodByKey(vm.SelectedPaymentMethod).PaymentMethod;
        var preparation = basket.SalePreparation();
        preparation.SavePaymentMethod(paymentMethod);

        // Authorise the payment
        var attempt = preparation.AuthorizePayment(paymentMethod.Key);

        // Redirect to receipt page having saved invoice key in session
        if (attempt.Payment.Success)
        {
            Session["InvoiceKey"] = attempt.Invoice.Key.ToString();
            return RedirectToUmbracoPage(GetReceiptPageNode().Id);
        }
        else
        {
            throw new ApplicationException("Payment authorisation failed.");
        }
    }

    return CurrentUmbracoPage();

As I say, works fine for the cash payment provider, but fails on the AuthorizePayment line with an error when I use the Authorize.Net one.  Looking into the source it's failing in the AuthorizeNetPaymentGatewayMethod.ProcessPayment method as no card details can be found.  That's expected really as I haven't provided any, so seems I'm missing a step somewhere as to where to hook in this extra part to the process.

Thanks in advance

Andy