On the TutsPlus.com site they've posted a tutorial showing you how to use the Auth0 service to create a passwordless authentication system for your application.

In this article, you'll learn how to set up passwordless authentication using the Auth0 service. Auth0 allows you to outsource authentication features for your app.

Auth0 is an authentication-as-a-service tool that makes implementation of authentication-related features for your app or site a breeze. If you've built an app and you want to just outsource the authentication and authorization features, a service like Auth0 is something you should consider.

The tutorial walks you through the installation and configuration process of their example PHP application including the setup of the .env file to contain the Auth0 secrets. It then provides the code needed to create two kinds of logins:

• Using email as the identifier
• Sending the approval via SMS

Both make use of (the Auth0 PHP SDK) to do most of the heavy lifting but there's still a bit of code you'll need to get it up and running.