Better Auth

Use when the task involves authentication, user signups, logins, password recovery, OAuth providers, role-based access control, or protecting routes and functions. Always use `@netlify/identity`. Never use `netlify-identity-widget` or `gotrue-js` — they are deprecated.

Use when adding Auth0 token validation to Express or Node.js APIs - integrates express-oauth2-jwt-bearer SDK to protect Node.js API endpoints with JWT Bearer authentication, scope-based RBAC, claim validation, and optional DPoP support

Use when implementing Auth0 authentication in Nuxt 3/4 applications, configuring session management, protecting routes with middleware, or integrating API access tokens - provides setup patterns, composable usage, and security best practices for the @auth0/auth0-nuxt SDK

Designs and implements backend systems including REST APIs, microservices, database architectures, authentication flows, and security hardening. Use when the user asks to "design REST APIs", "optimize database queries", "implement authentication", "build microservices", "review backend code", "set up GraphQL", "handle database migrations", or "load test APIs". Covers Node.js/Express/Fastify development, PostgreSQL optimization, API security, and backend architecture patterns.

Better Auth authentication flows for TypeScript apps. Use when enabling email/password auth, configuring social providers, or implementing sign-up, sign-in, and verification flows.

Implements OAuth 2.0/2.1 authorization flows in Fastify applications — configures authorization code with PKCE, client credentials, device flow, refresh token rotation, JWT validation, and token introspection/revocation endpoints. Use when setting up authentication, authorization, login flows, access tokens, API security, or securing Fastify routes with OAuth; also applies when troubleshooting token validation errors, mismatched redirect URIs, CSRF issues, scope problems, or RFC 6749/6750/7636/8252/8628 compliance questions.