I agree with you that we have widgets and functionality which are not documented. Our goal with launching the new documentation portal was to make everything we have easy to find. We also made it easy for the internal team to publish new articles, so that we can react faster to your feedback.
I'm sorry you haven't been able to find details information about the Login widget. We will document the properties, which are not mentioned (and also think about including a section with the rest of the widgets). Meanwhile if you have specific questions about the Login widget, I can answer them here. Thank you for the feedback.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items