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/models/user.py

@@ -0,0 +1,108 @@
+"""User model definitions"""
+
+from typing import Optional, List
+from pydantic import BaseModel, EmailStr, Field, ConfigDict
+from datetime import datetime
+from enum import Enum
+from bson import ObjectId
+
+
+class UserRole(str, Enum):
+    """User role enumeration"""
+    SYSTEM_ADMIN = "system_admin"
+    GROUP_ADMIN = "group_admin"
+    USER = "user"
+
+
+class PyObjectId(ObjectId):
+    """Custom ObjectId type for Pydantic"""
+    @classmethod
+    def __get_validators__(cls):
+        yield cls.validate
+
+    @classmethod
+    def validate(cls, v):
+        if not ObjectId.is_valid(v):
+            raise ValueError("Invalid ObjectId")
+        return ObjectId(v)
+
+    @classmethod
+    def __get_pydantic_json_schema__(cls, field_schema):
+        field_schema.update(type="string")
+
+
+class UserBase(BaseModel):
+    """Base user model"""
+    email: EmailStr
+    username: str = Field(..., min_length=3, max_length=50)
+    full_name: Optional[str] = None
+    role: UserRole = UserRole.USER
+    profile_picture: Optional[str] = None
+    phone_number: Optional[str] = None
+    gender: Optional[str] = None
+    birth_date: Optional[str] = None
+    is_active: bool = True
+    
+    model_config = ConfigDict(use_enum_values=True)
+
+
+class UserCreate(UserBase):
+    """User creation model"""
+    password: str = Field(..., min_length=8)
+
+
+class UserUpdate(BaseModel):
+    """User update model"""
+    email: Optional[EmailStr] = None
+    username: Optional[str] = Field(None, min_length=3, max_length=50)
+    full_name: Optional[str] = None
+    role: Optional[UserRole] = None
+    profile_picture: Optional[str] = None
+    phone_number: Optional[str] = None
+    gender: Optional[str] = None
+    birth_date: Optional[str] = None
+    is_active: Optional[bool] = None
+    password: Optional[str] = Field(None, min_length=8)
+
+
+class User(UserBase):
+    """User response model"""
+    id: str = Field(alias="_id")
+    created_at: datetime
+    updated_at: datetime
+    
+    model_config = ConfigDict(
+        populate_by_name=True,
+        arbitrary_types_allowed=True,
+        json_encoders={ObjectId: str}
+    )
+
+
+class UserInDB(User):
+    """User model in database"""
+    hashed_password: str
+
+
+class UserLogin(BaseModel):
+    """User login model"""
+    username: str
+    password: str
+
+
+class TokenData(BaseModel):
+    """Token data model"""
+    user_id: Optional[str] = None
+    username: Optional[str] = None
+    role: Optional[str] = None
+
+
+class Token(BaseModel):
+    """Token response model"""
+    access_token: str
+    refresh_token: str
+    token_type: str = "bearer"
+
+
+class TokenRefresh(BaseModel):
+    """Token refresh request model"""
+    refresh_token: str