silo sign-in

 silo sign-in  is (AKA social login ) a delegated sign-in/login service offered by silos such as Facebook Connect, Sign in with Google, and Log in with Twitter.

How not to
Instead of silo sign-in, you should use and support IndieAuth, and if you want to allow fallback to specific silos, support RelMeAuth with those silos that support OAuth.

Apple
Apple has Sign In with Apple

Facebook
Facebook has Facebook Connect

GitHub
GitHub does not have explicit documentation for use purely as a delegated sign-in/login service, however there is this documentation for designing/building your own GitHub application that makes use of GitHub authentication:
 * https://docs.github.com/en/developers/apps/building-github-apps/authenticating-with-github-apps#authenticating-as-a-github-app

In addition, others have documented guides for using GitHub for delegated sign-in:
 * GitLab: Use GitHub as an authentication
 * How to Integrate GitHub Login in your Website | WordPress | OAuth

Google
Google has Sign in with Google (part of Google Identity Platform)

Twitter
Twitter has Log in with Twitter