The makeBucket and checkIfBucketExists methods can use custom Attributes but the multipartUpload and download methods do not.
Why is this so?
It makes integration testing with localstack difficult.
Here is a demonstration project.
We have fixed a few bugs around attribute propagation in nested streams/operators the latest Akka versions, could be worth trying out latest (2.6.16) if an older Akka version is what you end up with out of the box without explicitly specifying a version.