A JavaScript library to use Netlify's OAuth providers, it relies on a popup (which may cause issues on mobile or with popup blockers e.g. in Firefox).
You can check an example React implementation/usage here: https://github.com/kentcdodds/react-github-profile/blob/b0c6a4628535fcea32f4f6617efd03f6b29574f4/src/github-client.js#L1
Full setup instructions can be found in the Netlify OAuth provider docs.
Lowest level JS Library: If you want to use the official Javascript bindings to GoTrue, Netlify's underlying Identity service written in Go, use https://github.com/netlify/gotrue-js
React bindings: If you want a thin wrapper over Gotrue-js for React, react-netlify-identity is a "headless" library, meaning there is no UI exported and you will write your own UI to work with the authentication. https://github.com/sw-yx/react-netlify-identity
High level overlay: If you want a "widget" overlay that gives you a nice UI out of the box, with a somewhat larger bundle, check https://github.com/netlify/netlify-identity-widget
High level popup: If you want a popup window approach also with a nice UI out of the box, and don't mind the popup flow, check https://github.com/netlify/netlify-auth-providers