Add user authentication to a Netlify site with @netlify/identity — signup/login/logout, Google/GitHub/GitLab/Bitbucket OAuth, server-side getUser() checks, role-based access control, and Identity event functions. Use it when a task involves adding a login or signup form, gating content to members or roles, "auth middleware" or verifying users in Netlify Functions or Edge Functions, handling OAuth or email-confirmation callbacks, assigning roles at signup, or customizing Identity emails. For locking a whole site to your company or employees-only access, use netlify-access-control instead.