I try to practice using User Authentication.
But it cannot work as I expected.
I expected that it can show the login interface to me.
STEPS:
1.use localhost:12345/login_page to connect the server
2.then show the login interface to me
3.key in the username and password
var express = require('express');
var cookieSession = require('cookie-session');
var app = express();
app.use(cookieSession({
    secret: 'session',
    keys: 'node'
}));
app.get('/login_page', function(req, res){
    if(!req.session.logined){
        res.send('<a href="http://127.0.0.1:12345/logout">Logout Now</a>');
        res.end();
        return;
    }
    res.send('<form action="http://localhost:12345/login" method="POST">');
    res.send('<input type="text" name="username">');
    res.send('<br/>');
    res.send('<input type="password" name="password">');
    res.send('<br/>');
    res.send('<input type="submit" value="login">');
    res.send('</form>');
    res.end();
});
app.post('/login', function(req, res){
    if(res.body.username != 'user' || 
       req.body.password != '12345678'){
        res.send('Account or password error, please login again');
        res.end();
        return;
    }
    res.session.logined = true;
    res.redirect('/login_page');
    res.end();
});
app.post('/logout', function(req, res){
    req.session.logined = false;
    res.redirect('/login');
    res.end();
});
app.listen(12345);
    
res.sendtwice. you should send the login page as ahtmlfile.