Google Auto Discount Integration

Merchello integrates with Google's automatic discount feature, which lets Google Shopping display discounted prices directly in search results. When a shopper clicks through from Google, the discount is automatically applied to their checkout session.

How It Works

Google Shopping can send shoppers to your site with a pv2 query parameter in the URL. This parameter contains a signed JWT token with discount information (discounted price, discount percentage, currency, offer ID, etc.).

Merchello's GoogleAutoDiscountMiddleware intercepts these requests, validates the token, and stores the discount information in an encrypted cookie so it persists through the checkout flow.

The Flow

1. Shopper sees discounted price on Google Shopping
2. Clicks through to your product page
   URL: https://yourstore.com/products/blue-widget?pv2=eyJhbGci...
3. GoogleAutoDiscountMiddleware intercepts the request
4. Validates the pv2 JWT against your configured merchant ID(s)
5. Stores discount info in an encrypted cookie (merchello_gad)
6. Redirects to the same URL without the pv2 parameter
7. On subsequent requests, restores discount from cookie
8. Checkout service applies the discount during basket calculation

Middleware Details

The middleware (GoogleAutoDiscountMiddleware) runs on every request and does two things:

On GET requests with a pv2 parameter

1. Looks up all product feeds that have an auto-discount merchant ID configured
2. Tries to validate the JWT token against each merchant ID
3. On successful validation, creates a GoogleAutoDiscountActiveDto with:
4. DiscountedPrice -- the price Google is advertising
5. DiscountPercentage -- the discount percentage
6. DiscountCode -- the discount code to apply
7. CurrencyCode -- the currency of the discounted price
8. OfferId -- the Google Shopping offer ID
9. PageExpiryUtc -- when the discount should stop showing on the page (30 minutes)
10. CheckoutExpiryUtc -- when the discount expires for checkout purposes (48 hours, or JWT expiry, whichever is sooner)
11. Sets the DTO on HttpContext.Items["MerchelloGoogleAutoDiscount"] for immediate use
12. Encrypts the DTO and stores it in a secure cookie
13. Redirects to the same URL without the pv2 parameter (to avoid bookmark/share issues)

On all other requests

1. Checks for the merchello_gad cookie
2. If found, decrypts and deserializes the discount data
3. Checks if the checkout expiry has passed -- if so, deletes the cookie
4. Otherwise, sets the DTO on HttpContext.Items for the checkout service to pick up

Cookie Security

The discount cookie uses multiple layers of protection:

Property	Value	Why
HttpOnly	true	Cannot be read by JavaScript
Secure	true	Only sent over HTTPS
SameSite	Lax	Allows the initial redirect from Google
IsEssential	true	Not affected by cookie consent (it is functional, not tracking)
Encryption	ASP.NET Data Protection	Cookie payload is encrypted using IDataProtectionProvider
Expiry	CheckoutExpiryUtc	Cookie auto-expires when the discount window closes

Expiry Windows

There are two expiry windows, and the shorter of each window or the JWT expiry is used:

Window	Duration	Purpose
Page display	30 minutes	How long the discounted price shows on product pages
Checkout	48 hours	How long the discount remains valid for checkout

Note: The JWT token from Google has its own expiry. Merchello uses whichever expires sooner -- the configured window or the JWT expiry.

Configuration

To enable Google auto discounts, you need:

1. A product feed configured in the Merchello backoffice with a Google Merchant Center merchant ID
2. Auto-discount settings enabled on that product feed
3. Products listed on Google Shopping with automatic discounts configured in Google Merchant Center

The middleware reads merchant IDs from enabled product feeds via IProductFeedService.GetAutoDiscountMerchantIdsAsync(). You do not need to configure merchant IDs separately -- they come from your product feed settings.

Reading the Discount in Your Code

The active discount (if any) is available via HttpContext.Items:

// In a controller or service with HttpContext access
var discount = httpContext.Items["MerchelloGoogleAutoDiscount"] as GoogleAutoDiscountActiveDto;
if (discount != null)
{
    // A Google auto discount is active
    var discountedPrice = discount.DiscountedPrice;
    var discountCode = discount.DiscountCode;
    var isPageExpired = discount.PageExpiryUtc <= DateTime.UtcNow;
    var isCheckoutExpired = discount.CheckoutExpiryUtc <= DateTime.UtcNow;
}

Tip: The page expiry and checkout expiry serve different purposes. You might want to stop showing the discounted price on the product page after 30 minutes (page expiry), but still honor the discount during checkout for up to 48 hours (checkout expiry).

Error Handling

The middleware is designed to be fault-tolerant. If anything goes wrong (invalid token, decryption failure, service error), it logs a warning and continues the request pipeline normally. A Google auto-discount failure should never prevent a customer from using your site.

Key Files

File	Description
Merchello/Middleware/GoogleAutoDiscountMiddleware.cs	The middleware implementation
Merchello.Core/ProductFeeds/Dtos/GoogleAutoDiscountActiveDto.cs	DTO stored in HttpContext and cookie
Merchello.Core/ProductFeeds/Services/Interfaces/IGoogleAutoDiscountService.cs	JWT validation service
Merchello.Core/ProductFeeds/Services/Interfaces/IProductFeedService.cs	Product feed service (merchant ID lookup)