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 implementations for React 19 / Next.js 15 stacks. ### Trigger Conditions - Working on login/signup flows, session management, or OAuth integrations. - Integrating Clerk, Supabase Auth, Auth.js v5, Better Auth, or Auth0. - Implementing RBAC (Role-Based Access Control) or ABAC. - Setting up WebAuthn/Passkeys, MFA/2FA, or SSO. - Securing Next.js App Router routes with middleware-based auth guards. --- ### Identity Provider Selection Guide | Provider | Best For | Key Strength | Pricing Model | |---|---|---|---| | **Clerk** | New SaaS products | Best developer DX, prebuilt UI components, orgs/teams out-of-the-box | Per MAU (free up to 10k) | | **Supabase Auth** | Existing Supabase apps | Native RLS integration, multi-provider OAuth, generous free tier | Included with Supabase | | **Auth.js v5** | Self-hosted control | Full data ownership, zero vendor lock-in, Edge-compatible | 100% Free / OSS | | **Better Auth** | Modern TS-first apps | Comprehensive TypeScript plugin ecosystem, 2FA, passkeys | 100% Fr...