auth-implementation-patternslisted

# Authentication & Authorization Implementation Patterns Build secure, scalable authentication and authorization systems using industry-standard patterns and modern best practices. ## When to Use This Skill - Implementing user authentication systems - Securing REST or GraphQL APIs - Adding OAuth2/social login - Implementing role-based access control (RBAC) - Designing session management - Migrating authentication systems - Debugging auth issues - Implementing SSO or multi-tenancy ## Core Concepts ### 1. Authentication vs Authorization **Authentication (AuthN)**: Who are you? - Verifying identity (username/password, OAuth, biometrics) - Issuing credentials (sessions, tokens) - Managing login/logout **Authorization (AuthZ)**: What can you do? - Permission checking - Role-based access control (RBAC) - Resource ownership validation - Policy enforcement ### 2. Authentication Strategies **Session-Based:** - Server stores session state - Session ID in cookie - Traditional, simple, stateful **Token-Based (JWT):** - Stateless, self-contained - Scales horizontally - Can store claims **OAuth2/OpenID Connect:** - Delegate authentication - Social login (Google, GitHub) - Enterprise SSO ## JWT Authentication ### Pattern 1: JWT Implementation ```typescript // JWT structure: header.payload.signature import jwt from 'jsonwebtoken'; import { Request, Response, NextFunction } from 'express'; interface JWTPayload { userId: string; email: string; role: string; iat: