You create a client application that interacts with Dataverse. You need to use the OAuth to access the Dataverse data. 
What should be your first step before you can authenticate your access to the data by using OAuth?

Answer options:

A.Use ADAL client libraries
B.Identify the OAuth provider
C.Use XrmTooling APIs
D.Register your application with Azure AD
E.Use the AccessToken

Correct Answer: D 
The OAuth 2.0 is the industry-standard security protocol. It is based on specific authorization flows for applications and devices that providers define. The providers` list includes Azure AD, Basecamp, Dropbox, GitHub, Google, Instagram, Facebook, Salesforce, and others. 
When you create a client application that uses the Dataverse data, you need to use the Azure AD as the identity provider. And in the client .Net code, you use the Azure Active Directory Authentication Libraries (ADAL) for Azure AD authentication. If the client application is Windows-based, you use the XmrTooling APIs for authentication. The result of the authentication is the access token. But you can use these libraries and get the token only after you register your application within your Azure AD tenant. There are two types of client applications you can register: Web app/API and Native. 
The Web app/API is an application that executes on the web server. The Native type is running natively on the device. 
All other options are incorrect. 
For more information about using the OAuth for the Dataverse authentication, please visit the below URL: 

https://docs.microsoft.com/en-us/powerapps/developer/data-platform/authenticate-oauth