Agent Skills: auth-system

Implement secure authentication and authorization systems with JWT, OAuth2, Session-based auth, and RBAC. Use when: (1) implementing user login/signup, (2) setting up JWT tokens, (3) OAuth2 integration (Google, GitHub, etc.), (4) role-based access control (RBAC), (5) password hashing and validation, (6) session management, (7) API authentication middleware, (8) 2FA/MFA setup. Triggers: "authentication", "login", "JWT", "OAuth", "session", "password hash", "RBAC", "permissions", "2FA".