docs: function get_user_account_id_for_credentials(username, password) {
  
      return new Promise((resolve, reject) => {
  
          dbMgr
              .find(app_config.get("app:db_collections:user_account"), {
                  "username": username,
                  "password": auth_util.encrypt_password(password)
              }, {"limit": 1})
              .then((accounts) => {
                  if (accounts.length > 0) {
                      return resolve(accounts[0]._id.toString());
                  } else {
                      return reject(new Error("Account not found."));
                  }
              }, reject);
      });
  }