Post request from client gives undefined (nodejs) - node.js

Question

I'm doing clienten post operation on my node js server, it works fine from postman, but clienten undefend returns
as i said from postman
{ "user": {
"email": "levlaaaaa#levla.com",
"password": "123" } }
When I throw the object, it works fine, but it returns undefined on the cilient side.
client request file (react)
const loginProccsess = async (e) => {
e.preventDefault()
const data = {
"user": {
"email":email,
"password": password
}
}
// return console.log(JSON.stringify(data))
await fetch("/api/auth/login", {
method: "POST",
mode: "cors",
// credentials: "some-origin",
header: {
"Content-type ": "application/json"
},
redirect: "follow",
body: JSON.stringify(data)
}).then((res) => {
console.log(res)
})
backend login.js (login router request)
router.post("/login", authOP, (req, res, next) => {
const { body: { user } } = req
const userLogin = new User();
console.log(user)
if (!user.email && !user.password) {
return res.status(402).json({
errors: "Eposta veya şifre zorunlu 😊 ! ",
});
}
return passport.authenticate('local', {
session: false,
successRedirect: '/home',
failureRedirect: '/login'
}, (err, passportUser, info) => {
if (err) {
return next(err)
}
if (passportUser) {
console.log(passportUser)
const user = passportUser
user.token = userLogin.generateJWT(user.email, user.id);
return res.json({ user: passportUser })
}
return res.status(400).json({ message: info });
})(req, res, next)
})
// app.js(server) (main file)
app.use(Sentry.Handlers.requestHandler());
app.use(cookieParser());
app.use(express.json())
app.use(cors());
app.use(session({
resave: false,
saveUninitialized: true,
secret: 'secret'
}))
app.use(passport.initialize())
app.use(passport.session())