nodejs didnt work session

I have a login page when I login its work and alert me "you login seccussfull". now I write after this message set a session to save username . when I login it works and console me but when I send another parameter to server and console it ,it is show empty! please help me ...

its my server.js(nodejs code)

var express = require('express');
var bodyParser = require("body-parser");
var session = require('express-session');
var app = express();

app.use(session({secret: "clicksite"}));

app.use(express.static(__dirname + "/static"));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));

var users = {clicksite: "12345", "clicksource": "1234"}; //key:value  users[clikcisite]=12345


app.get('/test', function (req, res, next) {
    console.log("test page");
    res.sendFile(__dirname + "/static/test.html");

    console.log(req.session);


});

app.post("/login", function (req, resp, next) {
    console.log(req.body);
    for (user in users) {
        console.log(users);
        if (req.body["user"] == user) {
            if (req.body["pass"] == users[user]) {
                resp.send("logined");
                req.session.auth = {username: req.body['user']};
                console.log(req.session);
                return;
            } else {
                resp.send("pass is wrong");
                return;
            }
        }
    }

    resp.send("user not found");
});

app.post("/signup", function (req, resp, next) {
    for (user in users) {
        console.log(req.body["username"]);
        if (req.body["username"] == user) {
            resp.send("this username not available");
        }
        else {
            users[req.body.username] = req.body.password;
            console.log(users);
            resp.send("you signupped seccussfull");
            req.session.user = "ali";
        }

    }
});


app.listen(8000);
console.log("server run on port 8000");

and its my function.js

$(document).ready(function () {
$("#login").click(function () {
    var user=$("#user").val();
    var pass=$("#pass").val();
    $.post("/login",{user:user,pass:pass},function (data) {
        alert(data.toString());
    })
});

$("#signup").click(function () {
    var user=$("#username").val();
    var pass=$("#password").val();
    $.post("/signup",{username:user,password:pass},function (data) {
        alert(data.toString());
    })
});

})

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