Ideally, I'd like to be able to press 1 button on my keyboard and have the screensaver come up, and not just a preview, but the actual screensaver such that when I try to access the computer it shows a login screen (as per my screensaver settings). I say this last part in particular because I don't want a shortcut to the "Preview" button, which doesn't seem to require me to log back in after the preview (which is contrary to my settings and what I'm looking for).
If a single button isn't possible (i.e. via some local mapping or keys or whatnot), perhaps a quick combination of keys?
If all else is not possible, it would be handy to be able to trigger my screensaver via a shortcut on my desktop.
Are any of these doable? If so, how?