How to send a verified custom request from shopify app frontend to backend.

[Masato338]

I want to send a verified request from app front to backend. However, I don't know how to determine which store sent the request. In the GET request when I load the app page, I can determine the store as shown below.

router.get("(.*)", async (ctx) => {
  const { shop, charge_id } = ctx.query;
}

But, I don't know how to give the store parameter to custom requests, and how to validate the request.

I'm referring to https://github.com/Shopify/shopify-app-node