How to log where documents on a Sharded MongoDB Cluster go?

Question

I set up a local Sharded MongoDB Cluster using Docker and configured a sharded collection. The cluster has 2 mongos, 3 config server (1 primary / 2 secondary), 6 shard server (2 shards with 1 primary / 2 secondary each). The sharded collection is working fine and the documents get splitt evenly between both shards.

Now I'm trying to find a way to log on which shard each document is stored.

Example: I store 3 documents A, B and C. The logs should tell me that A and C went to shard_0 and B went to shard_1.

How can this behavior be achieved?

More background: I'm using Spring as my backend and GridFS with sharded fs.chunks collection. I want to know on which shard the binary data of each file gets stored. Preferably I would like Spring to log where the files stored using GridFSTemplate go but it has no build in logging so I guess that's not something to get working easily.