Code Hanging on Acquire Token

I am attempting to acquire a token from AzureAD in a native app and while this works fine on a number of computers, I have one where the application just hangs. Here is the code:

public async Task<string> GetTokenAAD()

        {

            //example https://docs.microsoft.com/en-us/power-bi/developer/get-azuread-access-token

           var credential = new UserPasswordCredential(this.userName, this.password);

            var authenticationContext = new AuthenticationContext(Properties.Settings.Default.AADAUTH_URL);

            authenticationResult = await authenticationContext.AcquireTokenAsync(resourceUrl, this.clientID, credential); //code hangs here

            if (authenticationResult != null)

            {

                return authenticationResult.AccessToken;

            }

            return string.Empty;

        }