Rift Quest:Troll Bait  

Each camp has 2-4 cages in it, locked. Most Trolls (not all) have a Crude Key, good for opening only one cage before it breaks. So, kill a troll, open a cage. Rinse, repeat.

The keys look like they should be sttackable. We see no reason they would not, but we never saw them do it. It is possible you will not get a second key if you already have one in your bags. Kill, loot, release, rinse, repeat.