Apple Sign-in is based on OAuth 2.0 and OpenID Connect, and provides a privacy-friendly way for users to sign in to websites and apps.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
Ruby on Rails is a server-side web application framework written in Ruby under the MIT License.
RxJS is a reactive library used to implement reactive programming to deal with async implementation, callbacks, and event-based programs.
A modest JavaScript framework for the HTML you already have.