Is there an API for querying GRR users?

Can I somehow use the API to retrieve information about the GRR users and their labels? Currently, I am running `grr_config_updater show_user` and parsing its output, but that seems to incur a pretty high startup cost (between 2 and 3 seconds on a VM with SSD storage.) and I would rather not rely on parsing plain text output that may change at any time.