That is located in the belly of the College of Winterhold, by the atronarch forge? It says something about rings, but I haven't even found any lore in-game about it!

I believe it is for the conjuration Master quest (quest that unlocks when your conjuration reaches 100). I'm probably wrong, though...

There are quests for level 100 skills? what?

I take that back. It's not for that quest (though yes, there is a master quest that starts at level 90 for each magic school).

it is not the conjuration quest but a totally separate and unmarked quest. read the note in the same room, get the key and enjoy.

^^ Yeah, that.

get the key in the same room, go to the Arcaneum and look for the chest with the same name as your key, unlock it, take the rings, put them on the glove, help him, get reward... Bam