The documentation for authentication in the plugin doesn't match all other file-based Google plugins. It's also missing information about Credentials and using JSON content for the Service Account. Also, the doc for Authentication is wrong for Service Account File Path. Should be this to match all other plugins with these fields:
“Path on the local file system of the service account key used for authorization. Can be set to auto-detect when running on a Dataproc cluster. When running on other clusters, the file must be present on every node in the cluster.
Default is auto-detect.”