You may want to configure your Authsignal integration with Auth0 to use an internal user ID instead of defaulting to use the Auth0 user ID. If you are storing your own internal user ID in Auth0 - for example as user metadata - then you can pass this in your custom action code snippet. 
const {
  handleAuth0ExecutePostLogin,
  handleAuth0ContinuePostLogin,
} = require("@authsignal/node");

exports.onExecutePostLogin = async (event, api) => {
  const userId = event.user.user_metadata["your_internal_user_id"];

  await handleAuth0ExecutePostLogin(event, api, { userId });
};

exports.onContinuePostLogin = async (event, api) => {
  const userId = event.user.user_metadata["your_internal_user_id"];

  await handleAuth0ContinuePostLogin(event, api, { userId });
};
Passing an internal user ID here is recommended if you’re also tracking actions in other parts of your app not related to Auth0 login - you should always use a consistent identifier.