How to use Dynamics CRM 2016 Web Api from an external app for an IFD Deployment?

Hi,

We have deployed Dynamics crm 2016 IFD and our external app is able to use the Organization Service.

However we are not able to use the Dynamics Crm Web API.

I found this article which talks about using Web API for Online or IFD

But according to the article we need to create a new APP in Azure Active Directory and then use ADAL to authenticate and acquire an OAUTH token.

For IFD there is no Azure Active Directory so can someone please tell me how can I connect to WEB API for an IFD deployment.

Thanks in advance.