user with id xxx serialized
email: ...
password: ...
isAuthenticated: true
Session {
    path: '/',
    _expires: null,
    originalMaxAge: null,
    httpOnly: true },
    passport: {user: xxx } }

app.use(session({
  secret: 'test',
  saveUninitialized: false,
  resave: true
}));
app.use(passport.initialize());
app.use(passport.session());

router.get('/',function(req, res){
 console.log(req.user);
 console.log(req.session);
});

router.post('/login',passport.authenticate('local'), function(req,res)
{
 console.log(req.user);
 console.log(req.isAuthenticated());
 console.log(req.session);
});

passport.serializeUser(function(user, done) {
  console.log("user with id " + user._id + " serialized");
  done(null, user._id);
});

passport.deserializeUser(function(id, done) {
  console.log("deserializing user with id " + id + " ");
  User.findById(id, function(err, user) {
  done(err, user);
 });
});

componentDidMount(){
    var current_user = "";
    fetch("http://localhost:3001/users/", {
        method: "get",
        headers: {
            'Accept':'application/json',
            'Content-Type': 'application/json'
        }
    })
    .then( (response)=> response.json())
    .then( (response)=> {
        if(response.user!==current_user){
            current_user = response.user;
            this.setState({
                user: current_user
            }), ()=> console.log(response);
        }
    })
}