What are some alternatives?
Vue.js - Reactive Components for Modern Web Interfaces
Okta - Enterprise-grade identity management for all your apps, users & devices
Auth0 - Auth0 is a program for people to get authentication and authorization services for their own business use.
AngularJS - AngularJS lets you extend HTML vocabulary for your application. The resulting environment is extraordinarily expressive, readable, and quick to develop.
OneLogin - On-demand SSO, directory integration, user provisioning and more