I did try to post this on the support site but for whatever reason registration wasn't working. An excellent plugin but it doesn't work in Google Chrome. I don't know why. Fortunately if it didn't work even for me then I guess the admin area was safely blocked !

Installed and activated this Plug-in and it added a professional looking icon to the User Manager. However attempts to log in as another user simply produced and undefined error, i.e. "Error !" and no explanation as to the nature of the error.
On checking my Plug-ins (with the intention of uninstalling) I find there have been 4 Authentication Plug-ins created which when I try to uninstall them, produce the error message "Plugin Uninstall: Manifest File invalid or not found." This will become an irritation as I like a tidy admin.
To sum up. A nice idea but not yet ready for distribution.