要在FastAPI中使用JWT進行身份驗證，我們可以使用PyJWT庫來生成和驗證JWT令牌。以下是一個簡單的示例代碼，演示如何在FastAPI應用程序中使用JWT進行身份驗證：

from fastapi import FastAPI, Depends, HTTPException
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from passlib.context import CryptContext
from datetime import datetime, timedelta

app = FastAPI()

# 加密算法
SECRET_KEY = "your_secret_key"
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

# 密碼加密
pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

# 用戶數據模型
users = {
    "user1": {
        "username": "user1",
        "password": "$2b$12$4QaMelDZ6p8H7bVz5H3RAuRfWFd2cE4VAUZd0nJ9H6p9BTJp6kQF6",  # 加密后的密碼為password
        "disabled": False
    }
}

# 生成JWT令牌
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

# 驗證JWT令牌
def decode_access_token(token: str):
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        return payload
    except JWTError:
        raise HTTPException(status_code=401, detail="Invalid token")

# 使用OAuth2PasswordBearer進行身份驗證
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

# 身份驗證路由
@app.post("/token")
async def login(form_data: dict = Depends(oauth2_scheme)):
    user = users.get(form_data["username"])
    if user is None or not pwd_context.verify(form_data["password"], user["password"]):
        raise HTTPException(status_code=400, detail="Incorrect username or password")
    access_token_expires = timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    access_token = create_access_token(data={"sub": user["username"]}, expires_delta=access_token_expires)
    return {"access_token": access_token, "token_type": "Bearer"}

# 保護需要身份驗證的路由
@app.get("/protected")
async def protected_route(token: str = Depends(oauth2_scheme)):
    payload = decode_access_token(token)
    username = payload.get("sub")
    user = users.get(username)
    if user is None:
        raise HTTPException(status_code=400, detail="User not found")
    return user

在上面的示例中，我們首先定義了一個create_access_token函數來生成JWT令牌，然后定義了一個decode_access_token函數來驗證JWT令牌。接著使用OAuth2PasswordBearer類來創建一個OAuth2密碼驗證方案。然后我們定義了一個登錄路由/token來驗證用戶的用戶名和密碼，并生成JWT令牌。最后我們定義了一個受保護的路由/protected，使用Depends(oauth2_scheme)來進行身份驗證。

請注意，以上示例僅作為演示目的，實際項目中可能需要根據需要進行更多的安全性配置和優化。