A customer has been moved from Dynamics 365 on premise to Dynamics 365 online.
However, they have an on premise ASP.Net application integrated with their old dynamics 365 that they can only access while connected to the server or on a VPN (URL is servername:81/Page.aspx).
What would be the best way to integrate this .Net application so the customer can access it online? Can anyone point me in the right direction?