How to add users to mongoDB when new user's sign in

[stoplion]

@ax0nic

const { MongoClient } = require("mongodb");

exports.onExecutePostUserRegistration = async (event) => {
  const newUser = { sub: event.user.sub };
  const client = await MongoClient.connect(event.secrets.MONGO_DB);
  const db = client.db();
  await db.collection("users").insertOne(newUser);
  client.close();
};

Where do you put env vars in Auth0?