Session data are lost using express session - node.js

Question

I'm working in devMode with angularjs and express-session with cors middleware and I run frontend from localhost:4200 and backend from localhost:8080
In login request I set user data in session and then when I call "/api/contacts", the session user data is undefined.
I tried to save session with session.save() but it does not work.
I noticed that between calls sessionID changes.
I searched for hours on google but I have not found any solution.
this is the frontend call to "/api/contacts"
this.http.get(environment.apiUrl + '/api/contacts', {
withCredentials: true,
})
this is part of server.js
app.use(cors({origin: [
"http://localhost:4200"
], credentials: true,
}));
let sess = session({
secret: 'my secret',
resave: false,
saveUninitialized: false,
store: new MemoryStore({
checkPeriod: 60000 * 5 // prune expired entries every 24h
}),
cookie: {
secure: app.get('env') === 'production'?true:false,
maxAge: 60000 * 5 ,
}
})
app.use(sess)
// Initialize the app.
var server = app.listen(process.env.PORT || 8080, function () {
});
const authMiddleware = (req, res, next) => {
// here req.session.user IS undefined
if(req.session && req.session.user) {
next();
} else {
res.status(403).send({
status: 403,
errorMessage: 'You must be logged in.'
});
}
};
app.get("/api/contacts", authMiddleware,(req, res) => {
// some code will run if authMiddleware pass
});
app.post('/api/login', validatePayloadMiddleware, (req, res) => {
if (req.body.username === "xx.xxxx#xxxx.xxx" && req.body.password === "xxxxxxx")
{
let user = {
id: req.sessionID,
username: req.body.username,
firstName: "Fabio",
lastName: "Spadaro",
};
req.session.user = user;
req.session.save((err) => {
console.log(err)
});
return res.status(200).json(user);
}
else
{
let body = {
error: true,
errorMessage: 'Permission denied!'
};
return res.status(403).json(body);
}
});