ADAL.NET, delivered as a nuget package named Microsoft.IdentityModel.Clients.ActiveDirectory, is an authentication library which enables developers to acquire tokens from Azure AD (Active Directory) and ADFS, to be used to access Microsoft APIs or applications registered with Azure AD. ADAL.NET is available on several .NET platforms, including desktop, Universal Windows Platform, Xamarin / Android, Xamarin iOS, Portable Class Libraries, and .NET Core. It supports a number of authentication scenarios, involving native applications (desktop or device) or private applications (Web API). Authentication can leverage users credentials or application secrets.
Client credential authentication is used by a confidential client application such as a daemon or web service to access resources using its own identity, rather than the user’s identity. The application can use either a shared secret or a client certificate to authenticate itself. Learn more about service to service calls using client credentials.
Read about it on the Azure blog.