Got this question from a user per email. Though I would respond here so more could benefit from it.
Is there a way to get artifact metadata from the C# code?
Mender Artifacts are basically tar archives, which can be unpacked,
$ tar xvf test.mender version manifest header.tar data/0000.tar
The various files inside the Mender Artifact contain the metadata. You can find the full description of the Mender Artifact structure here