JWT 认证及其在 FastAPI 中的使用

fake_users_db = {
    "johndoe": {
        "username": "johndoe",
        "full_name": "John Doe",
        "email": "johndoe@example.com",
        "hashed_password": "$2b$12$EixZaYVK1fsbw1ZfbX3OXePaWxn96p36WQoeG6Lruj3vjPGga31lW",
        "disabled": False,
    }
}

from pydantic import BaseModel
from typing import Union

class Token(BaseModel):
    access_token: str
    token_type: str


class TokenData(BaseModel):
    username: Union[str, None] = None


class User(BaseModel):
    username: str
    email: Union[str, None] = None
    full_name: Union[str, None] = None
    disabled: Union[bool, None] = None


class UserInDB(User):
    hashed_password: str

from passlib.context import CryptContext
pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

def verify_password(plain_password, hashed_password):
    """
    校验密码是否正确
    将传入的明文密码与数据库中的哈希值进行比对
    """
    return pwd_context.verify(plain_password, hashed_password)


def get_password_hash(password):
    """获取传入的密码的哈希值"""
    return pwd_context.hash(password)


def get_user(db, username: str):
    """根据用户名从指定数据库中获取用户"""
    if username in db:
        user_dict = db[username]
        return UserInDB(**user_dict)


def authenticate_user(fake_db, username: str, password: str):
    """身份验证, 返回用户对象或者 False"""
    user = get_user(fake_db, username)
    if not user:
        return False
    if not verify_password(password, user.hashed_password):
        return False
    return user

SECRET_KEY = "09d25e094faa6ca2556c818166b7a9563b93f7099f6f0f4caa6cf63b88e8d3e7"
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

from datetime import datetime, timedelta
from jose import JWTError, jwt

def create_access_token(data: dict, expires_delta=None):
    """创建 jwt token"""
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.utcnow() + expires_delta
    else:
        expire = datetime.utcnow() + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    # 注意这里就用到了上面定义的 SECRET_KEY 和 ALGORITHM
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt

from fastapi import Depends, FastAPI, HTTPException, status
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")
@app.post("/token", response_model=Token)
async def login_for_access_token(form_data: OAuth2PasswordRequestForm = Depends()):
    """登录并获取 token"""
    # 通过用户名和密码获取用户, 如果用户不存在或者密码错误, 则抛出异常
    user = authenticate_user(fake_users_db, form_data.username, form_data.password)

    if not user:
        raise HTTPException(
            # 这部分是规范, 401 表示未授权
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Bearer"},
        )

    # 上面已经相当于进行了用户身份验证, 所以这里可以直接创建 token
    access_token_expires = timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    access_token = create_access_token(
        data={"sub": user.username}, expires_delta=access_token_expires
    )
    # 这里如何返回也是规范, 我们已在上面已经定义好了 response_model=Token
    return {"access_token": access_token, "token_type": "bearer"}

async def get_current_user(token: str = Depends(oauth2_scheme)):
    """依赖函数, 用于获取当前用户"""
    # 定义一个异常, 用于在用户身份验证失败时抛出
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )

    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        # 从 payload 中获取 username
        # 关于 sub 的解释, 可以参考文档
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = TokenData(username=username)
    except JWTError:
        raise credentials_exception
    user = get_user(fake_users_db, username=token_data.username)
    if user is None:
        raise credentials_exception
    return user

async def get_current_active_user(current_user: User = Depends(get_current_user)):
    """依赖函数, 用于获取当前活跃的用户,用到了上面的依赖函数 get_current_user
    为什么 current_user 可以是 User 类型而不是 get_current_user 返回的 UserInDB 类型呢?
    因为 UserInDB 类型是 User 类型的子类, 所以可以直接赋值给 User 类型的变量
    """
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user

@app.get("/users/me/", response_model=User)
async def read_users_me(current_user: User = Depends(get_current_active_user)):
    """获取当前用户信息"""
    return current_user