How to make the callback URL secure

To make the callback URL secure, follow the flow below:

1. Check the incoming IP address of the sender.  https://developer.coingate.com/docs/payment-callback#ip-addresses
2. Use token parameter when creating an order. https://developer.coingate.com/docs/create-order
3. Do a double check when receiving the callback: take the order ID from the callback and call https://developer.coingate.com/docs/get-order to check current order status and amount