Using a hash (specifically with HMAC) provides a very secure way to ensure data is not modified. So your FoxyCart add-to-cart links and forms can be locked down, preventing any user from modifying them.
More information on FoxyCart and HMAC can be found on the FoxyCart HMAC page.
This plugin requires a FoxyCart account. FoxyCart is a hosted cart & payment page allow you to sell anything, using your existing website or platform. For more information, visit FoxyCart.
To install this plugin, search for its package name on the Plugin Store and click “Install”.