feat: OAuth 2.0 백엔드 시스템 구현 완료

Phase 1 & 2 완료:
- 프로젝트 기본 구조 설정
- Docker Compose 환경 구성 (MongoDB, Redis, Backend, Frontend)
- FastAPI 기반 OAuth 2.0 백엔드 구현

주요 기능:
- JWT 기반 인증 시스템
- 3단계 권한 체계 (System Admin/Group Admin/User)
- 사용자 관리 CRUD API
- 애플리케이션 관리 CRUD API
- OAuth 2.0 Authorization Code Flow
- Refresh Token 관리
- 인증 히스토리 추적

API 엔드포인트:
- /auth/* - 인증 관련 (register, login, logout, refresh)
- /users/* - 사용자 관리
- /applications/* - 애플리케이션 관리
- /oauth/* - OAuth 2.0 플로우

보안 기능:
- bcrypt 비밀번호 해싱
- JWT 토큰 인증
- CORS 설정
- Rate limiting 준비

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

oauth/backend/app/utils/security.py

@@ -0,0 +1,93 @@
+"""Security utilities for password hashing and JWT tokens"""
+
+from datetime import datetime, timedelta, timezone
+from typing import Optional, Dict, Any
+from passlib.context import CryptContext
+from jose import JWTError, jwt
+from app.config import settings
+import secrets
+import string
+
+# Password hashing context
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """Verify a plain password against a hashed password"""
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def hash_password(password: str) -> str:
+    """Hash a password"""
+    return pwd_context.hash(password)
+
+
+def create_access_token(data: Dict[str, Any], expires_delta: Optional[timedelta] = None) -> str:
+    """Create a JWT access token"""
+    to_encode = data.copy()
+    
+    if expires_delta:
+        expire = datetime.now(timezone.utc) + expires_delta
+    else:
+        expire = datetime.now(timezone.utc) + timedelta(
+            minutes=settings.jwt_access_token_expire_minutes
+        )
+    
+    to_encode.update({"exp": expire, "type": "access"})
+    encoded_jwt = jwt.encode(
+        to_encode,
+        settings.secret_key,
+        algorithm=settings.jwt_algorithm
+    )
+    return encoded_jwt
+
+
+def create_refresh_token(data: Dict[str, Any], expires_delta: Optional[timedelta] = None) -> str:
+    """Create a JWT refresh token"""
+    to_encode = data.copy()
+    
+    if expires_delta:
+        expire = datetime.now(timezone.utc) + expires_delta
+    else:
+        expire = datetime.now(timezone.utc) + timedelta(
+            days=settings.jwt_refresh_token_expire_days
+        )
+    
+    to_encode.update({"exp": expire, "type": "refresh"})
+    encoded_jwt = jwt.encode(
+        to_encode,
+        settings.secret_key,
+        algorithm=settings.jwt_algorithm
+    )
+    return encoded_jwt
+
+
+def decode_token(token: str) -> Optional[Dict[str, Any]]:
+    """Decode and verify a JWT token"""
+    try:
+        payload = jwt.decode(
+            token,
+            settings.secret_key,
+            algorithms=[settings.jwt_algorithm]
+        )
+        return payload
+    except JWTError:
+        return None
+
+
+def generate_client_secret() -> str:
+    """Generate a secure client secret"""
+    alphabet = string.ascii_letters + string.digits
+    return ''.join(secrets.choice(alphabet) for _ in range(32))
+
+
+def generate_client_id() -> str:
+    """Generate a unique client ID"""
+    alphabet = string.ascii_lowercase + string.digits
+    return ''.join(secrets.choice(alphabet) for _ in range(16))
+
+
+def generate_authorization_code() -> str:
+    """Generate a secure authorization code"""
+    alphabet = string.ascii_letters + string.digits
+    return ''.join(secrets.choice(alphabet) for _ in range(32))