We have a sales channel that we maintain and we would like to make secure calls to our API by issuing a merchant an API key (from us) which they can enter into an input within the sales channel app and store it securely so we can then use it to send calls to our API and ensure it is from the merchant associated with that key.
We already have the access token that Shopify send to us but this key will be something we provide to the merchant.
How can we securely store this key within Shopify and ensure it is not exposed in anyway?