https://github.com/OfficeDev/PnP/tree/master/Samples/Core.SitePermissions
O365/SharePoint Online
In Program.cs, at List<UserEntity> admins = cc.Web.GetAdministrators();
I get:
"An unhandled exception of type 'System.Xml.XmlException' occurred in System.Xml.dll
Additional information: For security reasons DTD is prohibited in this XML document. To enable DTD processing set the DtdProcessing property on XmlReaderSettings to Parse and pass the settings into XmlReader.Create method."
I think it is failing to authenticate. I think it isn't even sending an authentication header (according to what I see in Fiddler).
