Managed authentication service, client framework, and building blocks for developers who want to create user authentication experiences.
Authpack provides a custom auth API which can be added to your app in moments. It also provide a pre-made authentication solution so that you don't have to build your own auth system.
Handles auth entirely client-side with no cloud functions or anything required.
Netlify Identity service brings a full suite of authentication functionality, backed by the GoTrue API.