Store the Auth0 user id in a protected endpoint

In the example auth0 provides for Storing an Auth0 user id in a remote system it posts to an unprotected endpoint. Are there headers or something I can add to the request that my endpoint can check to make sure not just anyone can post a email and create a user?

const axios = require("axios");

 * @param {Event} event - Details about registration event.
exports.onExecutePostUserRegistration = async (event) => {
  await"", { params: { email: }});