I used Google+ so that you wouldn't need to create a user id / password. Each tag that you create is "owned" by you, and you probably wouldn't want other people to edit it (though there is an option to "unlock" a tag so that they can). It doesn't user your Google+ info, it's just for verification

For creation and updating, I can see why you would want to authenticate and authorize users, but there should should still be a way to have the app go into a read only state if all I want to do is scan.