NullReferenceExection when calling authenticationContext.AcquireTokenAsync

[cobra2020]

I am attempting an app_owns_data embedded PowerBI integration using the sample code from

https://github.com/Microsoft/PowerBI-Developer-Samples/tree/master/App%20Owns%20Data

I registered the application and added the applicationId to web.config.  In addition, specified the username and pwd of the master account.

On the Azure side, I configured the ADD permissions as shown below (see checked items in first image).

When authenticationContext.AcquireTokenAsync is invoked, I get the exception listed above.

Code:

// AuthorityUrl = https://login.microsoftonline.com/common/
// ResourceUrl = https://analysis.windows.net/powerbi/api
var authenticationContext = new AuthenticationContext(AuthorityUrl);
var credential = new UserPasswordCredential(Username, Password);
authenticationResult = authenticationContext.AcquireTokenAsync(ResourceUrl, ApplicationId, credential).Result;

Pictures below:

1. The AD permissions in Azure Portal

2. The NullReferenceException settings dialog

3. The top portion of the call-stack.

The version of Microsoft.IdentityModel.Clients.ActiveDirectory I use is the one form GitHub, v4.5.0.  In addition, Microsoft.PowerBI.Api is v2.4.0, but that is irrelevant here as I do not even got to the point of using it.

Has anyone experienced this?