In theory inside UUID v3 you should put a URL which is itself unique. Of course you can also put your MD5/SHA hash but I would consider deeply the objections I have made in my answer before taking this path.

If it is random unique hash data why not trusting the UUID's own generation of random unique hash data? Otherwise why not using your random hash/data as key and leaving UUID alone? I think I'm not catching fully your intent.

Why then net command doesn't show "Authenticated Users" in the users of mike? what is Authenticated Users? a group or something else? I get your point but your answer makes the whole thing look even more arcane.

see my edit, anyway it correctly shows groups caesar under mike's groups.

That's exactly my point, it should list all groups but it doesn't! My "the command net cannot know it but mike also belongs to the Authenticated Users group" is a stating of the facts under Windows 7.