`--token` is deprecated

[MiroStW]

When using the snippet I get a warning

Authenticating with `--token` is deprecated and will be removed in a future major version of `firebase-tools`. Instead, use a service account key with `GOOGLE_APPLICATION_CREDENTIALS`: https://cloud.google.com/docs/authentication/getting-started

at this line:

snippets-node/firestore/solution-deletes/functions/index.js

Line 67 in ea3747e

token: functions.config().fb.token

Is that because I am using it in a wrong way or is the snipped outdated? How would I use the described service account key in the case of this snippet? I appreciate your help, I am still new to GCP!!

Environment:
firebase-tools: 11.20.0
Node: 16

Steps to reproduce:
use the snipped as described

Expected behaviour:
Execute recursive delete of path

Actual behaviour:
Same, but with deprecation warning