The requirement of internet connection for the Virtual DataPort (VDP) server depends on the fact whether the VDP server and Sharepoint server are on the same network or not. If they are on the same network, then the internet connection is not required. If they are not on the same network, then an internet connection is required by the VDP server to establish a remote connection to access the Excel file.
I implemented the following steps to create Excel data source in Denodo from excel sheet in SharePoint :
1. Generated client application token by going to** Azure Portal > App Registrations > New Registrations**.
1. Created a Client Secret Key by going to **Azure Portal > Certificates & Secrets > New Client Secret** or by going to **Azure Portal > Overview > Add a certificate or secret **
1. Created the new Excel data source by going to **File > New > Data Source > Excel** such that **File Location** is* HTTP Client* and **Authentication** as *OAuth 2.0 Authentication*.
You can refer to the document [How to Access Excel & Demilied Files In SharePoint From Denodo](https://community.denodo.com/kb/en/view/document/How%20to%20access%20Excel%20and%20Delimited%20Files%20in%20SharePoint%20from%20Denodo?category=Data%20Sources) to get all the detailed information on above steps.
Hope this helps!