We have a working solution for custom Excel import into SharePoint Online list. It was developed as Provider-hosted add in and its being hosted on Azure App Service.
Right now Azure App Service is allowing access from all internet but we need to restrict this access to only specific IPs - my question is what ranges should I restrict it to work with SharePoint Online. Is this the only list I should focus on: https://docs.microsoft.com/en-us/office365/enterprise/urls-and-ip-address-ranges
We already had a problem with that restrictions thats why it is opened to 'internet' but right now because of the policy this needs to be addressed.