Shopify: Open Redirect in shopify app URL

Hi, The Amazon Alexa app when installing calls a URL https://assistant-client.meteorapp.com/shopify/callback?code=6aae881ab9c4f12d5b264e6c871a108a&hmac=6109806a12b0439d6a2dce2d547344eb1c2c53e9691259f39eefbb93b9c9c97b&shop=pappuza-2.myshopify.com&timestamp=1494008598 The shop parameter will accept...