fastapi token 如何实现token有效时长更新

要实现FastAPI token有效时长更新，可以使用以下步骤：

在创建token时，添加一个expires_delta参数，用于设置token的有效时长，例如：

from datetime import timedelta
from fastapi import Depends, FastAPI
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def create_access_token(data: dict, expires_delta: timedelta = None):
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.utcnow() + expires_delta
    else:
        expire = datetime.utcnow() + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt

在验证token时，检查token是否过期，并且如果token即将过期，则更新token的有效时长，并返回新的token，例如：

from datetime import datetime, timedelta
from fastapi import Depends, FastAPI, HTTPException, status
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from jose import JWTError, jwt

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def create_access_token(data: dict, expires_delta: timedelta = None):
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.utcnow() + expires_delta
    else:
        expire = datetime.utcnow() + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt

async def get_current_user(token: str = Depends(oauth2_scheme)):
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        username: str = payload.get("sub")
        if username is None:
            raise HTTPException(
                status_code=status.HTTP_401_UNAUTHORIZED,
                detail="Invalid authentication credentials",
                headers={"WWW-Authenticate": "Bearer"},
            )
    except JWTError:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid authentication credentials",
            headers={"WWW-Authenticate": "Bearer"},
        )

    # check if token is about to expire
    expire_time = datetime.fromtimestamp(payload['exp'])
    remaining_time = expire_time - datetime.utcnow()
    if remaining_time < timedelta(minutes=5):  # if token expires in less than 5 minutes
        new_token = create_access_token(data={"sub": username}, expires_delta=timedelta(minutes=30))
        return (username, new_token)
    else:
        return (username, token)

在get_current_user函数中，通过jwt.decode方法解码token，并检查token是否过期。如果token即将过期，则使用create_access_token方法创建一个新的token，并返回新的token和用户名。否则，返回原始的token和用户名。在调用get_current_user函数时，可以使用Depends(get_current_user)来获取当前用户和token。

这样，就可以实现FastAPI token有效时长的更新。