Only problem is that, at the moment, it does not work on joomla 3.x, although that is being worked on.
Thanks for this great free extension.
Unfortunataly I found that, once logged in, a log out button is needed, and maybe some info. When a user is logged in, only his picture is displayed, nothing more, not even his name. Hopefully that will be added in the future.
Also has a nice backend to check out which users logged in, and you can even get their emails and basic info for several stuff.
I'll be looking forward for more development on this one!