How to set credentialSecret asynchronously?

Node-RED is what I really need now.
I really enjoy to learn about Node-RED.

I'm trying to make a Node-RED app on Google Cloud Platform.
I succeeded to invoke some Google APIs with Compute Engine default service account.
So, I don't need credentials to invoke APIs on GCP, but I have to embed some credentials to invoke another APIs outside GCP.
Then, I consider to use key management server like Google Secret Manager to hide credentialSecret setting.
Is there a way to set credentialSecret asynchronously like below?

in settings.js

module.exports = {
  credentialSecret: async () => {
    // Access KMS with Compute Engine default service account
    ...
    return encryptionKey;
  },
}

Or, set credentialSecret value on boot before starting Node-RED?

Thanks.