The plugin configuration belongs in @PLUGIN@.config. The credentialsPath is required when not using the Spanner emulator.
[ref-database "spanner"]
instance = spanner-instance
database = global-refdb
useEmulator = false
credentialsPath = credentials.json
ref-database.spanner.instance : Optional. The name of the spanner instance. Default: spanner-instance.
ref-database.spanner.database : Optional. The name of the spanner database. Default: global-refdb.
ref-database.spanner.useEmulator : Optional. Boolean, whether or not to use the in-memory Cloud Spanner emulator. Default: false.
ref-database.spanner.credentialsPath : Required when not using the emulator. The name of the google cloud credentials file in the site/etc directory. Default: null.