serialize-flow

passport.authenticate()-----------
                                 |  
                                 |  invokes 
                                \./
       passport.use(new LocalStrategy(
            function(username, password, done) {

           // match req.body.username and req.body.password from any 
              //data base or in memory array
               if(user_is_found_and_pass_match)
                  done(null,user);--
               else                   | *1-user passed
                                      |
                  done(null,false);---| *2-user not passed
       });                            | 
                                      |return back to
passport.authenticate() <------------ |
                      |
                      |----- if user is passed in done() (*1) ,   
                            |
    req.login()   <--------- 
              |
 //authenticate() middleware  may  invoke req.login() automatically.
              |
              | calls
             \./  
 passport.serializeUser(function(user, done) {
        done(null, user.id); 
                     |
//use 'id'to serialize, you can use other or user object itself
    });              |-->saved to session req.session.passport.user = {id:'..'}
                     |
                     |__________________
                                       |          
    passport.deserializeUser(function(id, done) {
                      ________________|
                      | 
        User.findById(id, function(err, user) {
            done(err, user);
                       |______________>user object ataches to the request as req.user

     });
});