authentication-identity-expert

# Authentication & Identity Expert (2026 Edition) [English](#english) | [Bahasa Indonesia](#bahasa-indonesia) --- <a name="english"></a> ## English ### Description Production-grade guide for implementing secure authentication, authorization, and identity management in modern web and mobile applications. Covers **Clerk**, **Supabase Auth**, **Auth.js v5**, **Better Auth**, JWT patterns, OAuth 2.1, PKCE flows, RBAC/ABAC, passkeys (WebAuthn), and MFA implementation for React 19 / Next.js 15 stacks. ### Trigger Conditions - Working on login/signup flows, session management, or OAuth integration. - Integrating **Clerk**, **Supabase Auth**, **Auth.js v5**, **Better Auth**, or **Auth0**. - Implementing **Role-Based Access Control (RBAC)** or **Attribute-Based Access Control (ABAC)**. - Setting up **WebAuthn/Passkeys**, **MFA/2FA**, or **SSO**. - Securing Next.js App Router routes with middleware-based auth guards. - Implementing **OAuth 2.1** flows with PKCE for SPAs or mobile apps. --- ### Identity Provider Selection Guide (2026) | Provider | Best For | Key Strength | |---|---|---| | **Clerk** | SaaS, B2B apps | Built-in organizations, roles, MFA, UI components | | **Supabase Auth** | Supabase-powered apps | RLS integration, social login, SSO | | **Auth.js v5** | Next.js self-hosted | Flexible adapters, edge-compatible | | **Better Auth** | TypeScript-first self-hosted | Modern DX, built-in 2FA, org management | | **Auth0** | Enterprise, compliance | Enterprise SSO, complia...