4 files changed, 403 insertions, 0 deletions
diff --git a/backend/app/auth/__init__.py b/backend/app/auth/__init__.py
new file mode 100644
index 0000000..8234b6f
--- /dev/null
+++ b/backend/app/auth/__init__.py
@@ -0,0 +1,17 @@
+from .routes import router as auth_router
+from .routes import get_current_user, get_current_user_optional
+from .models import User, get_db, init_db
+from .utils import Token, UserCreate, UserResponse
+
+__all__ = [
+    'auth_router',
+    'get_current_user',
+    'get_current_user_optional',
+    'User',
+    'get_db',
+    'init_db',
+    'Token',
+    'UserCreate',
+    'UserResponse',
+]
+
diff --git a/backend/app/auth/models.py b/backend/app/auth/models.py
new file mode 100644
index 0000000..8477ba2
--- /dev/null
+++ b/backend/app/auth/models.py
@@ -0,0 +1,44 @@
+import os
+from sqlalchemy import Column, Integer, String, DateTime, Text, create_engine
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import sessionmaker
+from datetime import datetime
+
+# Database configuration
+DATA_ROOT = os.path.abspath(os.getenv("DATA_ROOT", os.path.join(os.getcwd(), "data")))
+DATABASE_PATH = os.path.join(DATA_ROOT, "users.db")
+DATABASE_URL = f"sqlite:///{DATABASE_PATH}"
+
+engine = create_engine(DATABASE_URL, connect_args={"check_same_thread": False})
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+Base = declarative_base()
+
+
+class User(Base):
+    __tablename__ = "users"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    username = Column(String(50), unique=True, index=True, nullable=False)
+    email = Column(String(100), unique=True, index=True, nullable=False)
+    hashed_password = Column(String(255), nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    is_active = Column(Integer, default=1)
+    # API Keys (stored encrypted in production, plain for simplicity here)
+    openai_api_key = Column(Text, nullable=True)
+    gemini_api_key = Column(Text, nullable=True)
+
+
+def init_db():
+    """Initialize database tables"""
+    os.makedirs(DATA_ROOT, exist_ok=True)
+    Base.metadata.create_all(bind=engine)
+
+
+def get_db():
+    """Dependency to get database session"""
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
diff --git a/backend/app/auth/routes.py b/backend/app/auth/routes.py
new file mode 100644
index 0000000..3c906b5
--- /dev/null
+++ b/backend/app/auth/routes.py
@@ -0,0 +1,269 @@
+from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
+from sqlalchemy.orm import Session
+from typing import Optional
+from pydantic import BaseModel
+
+from .models import User, get_db
+from .utils import (
+    Token, UserCreate, UserLogin, UserResponse,
+    verify_password, get_password_hash, create_access_token, decode_token
+)
+
+router = APIRouter(prefix="/api/auth", tags=["Authentication"])
+
+# OAuth2 scheme for token extraction
+oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login", auto_error=True)
+oauth2_scheme_optional = OAuth2PasswordBearer(tokenUrl="/api/auth/login", auto_error=False)
+
+
+async def get_current_user(
+    token: str = Depends(oauth2_scheme),
+    db: Session = Depends(get_db)
+) -> User:
+    """
+    Dependency: Validate JWT token and return current user.
+    Raises 401 if token is invalid or user not found.
+    """
+    username = decode_token(token)
+    if not username:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid or expired token",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+    
+    user = db.query(User).filter(User.username == username).first()
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="User not found",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+    
+    if not user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="User account is disabled"
+        )
+    
+    return user
+
+
+async def get_current_user_optional(
+    token: Optional[str] = Depends(oauth2_scheme_optional),
+    db: Session = Depends(get_db)
+) -> Optional[User]:
+    """
+    Dependency: Try to get current user, but don't fail if not authenticated.
+    Returns None if no valid token.
+    """
+    if not token:
+        return None
+    
+    username = decode_token(token)
+    if not username:
+        return None
+    
+    user = db.query(User).filter(User.username == username).first()
+    if not user or not user.is_active:
+        return None
+    
+    return user
+
+
+@router.get("/check-username/{username}")
+async def check_username(username: str, db: Session = Depends(get_db)):
+    """
+    Check if a username is available.
+    """
+    existing = db.query(User).filter(User.username == username).first()
+    return {"available": existing is None}
+
+
+@router.get("/check-email/{email}")
+async def check_email(email: str, db: Session = Depends(get_db)):
+    """
+    Check if an email is available.
+    """
+    existing = db.query(User).filter(User.email == email).first()
+    return {"available": existing is None}
+
+
+@router.post("/register", response_model=UserResponse, status_code=status.HTTP_201_CREATED)
+async def register(user_data: UserCreate, db: Session = Depends(get_db)):
+    """
+    Register a new user account.
+    """
+    # Check if username already exists
+    existing_user = db.query(User).filter(User.username == user_data.username).first()
+    if existing_user:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Username already registered"
+        )
+    
+    # Check if email already exists
+    existing_email = db.query(User).filter(User.email == user_data.email).first()
+    if existing_email:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Email already registered"
+        )
+    
+    # Validate password length
+    if len(user_data.password) < 6:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Password must be at least 6 characters"
+        )
+    
+    # Create new user
+    user = User(
+        username=user_data.username,
+        email=user_data.email,
+        hashed_password=get_password_hash(user_data.password)
+    )
+    db.add(user)
+    db.commit()
+    db.refresh(user)
+    
+    return user
+
+
+@router.post("/login", response_model=Token)
+async def login(form_data: OAuth2PasswordRequestForm = Depends(), db: Session = Depends(get_db)):
+    """
+    Login with username and password, returns JWT token.
+    """
+    # Find user by username
+    user = db.query(User).filter(User.username == form_data.username).first()
+    
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect username or password",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+    
+    if not verify_password(form_data.password, user.hashed_password):
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect username or password",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+    
+    if not user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="User account is disabled"
+        )
+    
+    # Create access token
+    access_token = create_access_token(data={"sub": user.username})
+    
+    return {
+        "access_token": access_token,
+        "token_type": "bearer",
+        "username": user.username
+    }
+
+
+@router.post("/login/json", response_model=Token)
+async def login_json(user_data: UserLogin, db: Session = Depends(get_db)):
+    """
+    Login with JSON body (alternative to form-data).
+    """
+    # Find user by username
+    user = db.query(User).filter(User.username == user_data.username).first()
+    
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect username or password",
+        )
+    
+    if not verify_password(user_data.password, user.hashed_password):
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect username or password",
+        )
+    
+    if not user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="User account is disabled"
+        )
+    
+    # Create access token
+    access_token = create_access_token(data={"sub": user.username})
+    
+    return {
+        "access_token": access_token,
+        "token_type": "bearer",
+        "username": user.username
+    }
+
+
+@router.get("/me", response_model=UserResponse)
+async def get_me(current_user: User = Depends(get_current_user)):
+    """
+    Get current authenticated user's info.
+    """
+    return current_user
+
+
+@router.get("/api-keys")
+async def get_api_keys(current_user: User = Depends(get_current_user)):
+    """
+    Get current user's API keys (masked for security).
+    """
+    def mask_key(key: str | None) -> str:
+        if not key:
+            return ""
+        if len(key) <= 8:
+            return "*" * len(key)
+        return key[:4] + "*" * (len(key) - 8) + key[-4:]
+    
+    return {
+        "openai_api_key": mask_key(current_user.openai_api_key),
+        "gemini_api_key": mask_key(current_user.gemini_api_key),
+        "has_openai_key": bool(current_user.openai_api_key),
+        "has_gemini_key": bool(current_user.gemini_api_key),
+    }
+
+
+class ApiKeysUpdate(BaseModel):
+    openai_api_key: Optional[str] = None
+    gemini_api_key: Optional[str] = None
+
+
+@router.post("/api-keys")
+async def update_api_keys(
+    keys: ApiKeysUpdate,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db)
+):
+    """
+    Update current user's API keys.
+    Pass empty string to clear a key, or omit to keep unchanged.
+    """
+    if keys.openai_api_key is not None:
+        current_user.openai_api_key = keys.openai_api_key if keys.openai_api_key else None
+    
+    if keys.gemini_api_key is not None:
+        current_user.gemini_api_key = keys.gemini_api_key if keys.gemini_api_key else None
+    
+    db.commit()
+    
+    return {"message": "API keys updated successfully"}
+
+
+@router.post("/logout")
+async def logout():
+    """
+    Logout endpoint (client should discard the token).
+    JWT tokens are stateless, so this is just for API completeness.
+    """
+    return {"message": "Successfully logged out"}
+
diff --git a/backend/app/auth/utils.py b/backend/app/auth/utils.py
new file mode 100644
index 0000000..5889279
--- /dev/null
+++ b/backend/app/auth/utils.py
@@ -0,0 +1,73 @@
+import os
+import bcrypt
+from datetime import datetime, timedelta
+from typing import Optional
+from jose import JWTError, jwt
+from pydantic import BaseModel, EmailStr
+
+# Configuration - use environment variables in production
+SECRET_KEY = os.getenv("JWT_SECRET_KEY", "contextflow-secret-key-change-in-production-2024")
+ALGORITHM = "HS256"
+ACCESS_TOKEN_EXPIRE_MINUTES = int(os.getenv("JWT_EXPIRE_MINUTES", "1440"))  # 24 hours default
+
+
+# Pydantic models for request/response
+class Token(BaseModel):
+    access_token: str
+    token_type: str
+    username: str
+
+
+class TokenData(BaseModel):
+    username: Optional[str] = None
+
+
+class UserCreate(BaseModel):
+    username: str
+    email: EmailStr
+    password: str
+
+
+class UserLogin(BaseModel):
+    username: str
+    password: str
+
+
+class UserResponse(BaseModel):
+    id: int
+    username: str
+    email: str
+    created_at: datetime
+    is_active: int
+
+    class Config:
+        from_attributes = True
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """Verify a password against its hash"""
+    return bcrypt.checkpw(plain_password.encode('utf-8'), hashed_password.encode('utf-8'))
+
+
+def get_password_hash(password: str) -> str:
+    """Hash a password"""
+    return bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt()).decode('utf-8')
+
+
+def create_access_token(data: dict, expires_delta: Optional[timedelta] = None) -> str:
+    """Create a JWT access token"""
+    to_encode = data.copy()
+    expire = datetime.utcnow() + (expires_delta or timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES))
+    to_encode.update({"exp": expire})
+    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
+
+
+def decode_token(token: str) -> Optional[str]:
+    """Decode a JWT token and return the username"""
+    try:
+        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+        username: str = payload.get("sub")
+        return username
+    except JWTError:
+        return None
+