$this->Auth->User(); is null - cakephp

Question

I am new in cake php.
I am using cakephp 3.6.2 in linux ubuntu.
I use cakephp auth component.
While i give correct credentials it redirect back to the login page otherwise says error message "invalid username and password".
I debug and check details while i give correct credentials. It Set " $this->Auth->setUser($user);" correctly.
But After redirect " return $this->redirect($this->Auth->redirectUrl());"
$this->Auth->User() is Null and it redirects back to login page.
My Code
AppController.php
public function initialize(){
$this->loadComponent('RequestHandler');
$this->loadComponent('Flash');
$this->loadComponent('Auth', [
'authenticate' => [
'Form' => [
'fields' => ['username' => 'email', 'password' => 'password']
]
],
'loginAction' => ['controller' => 'Users', 'action' => 'login']
]);}
UserCOntroller.php
public function login()
{
if ($this->request->is('post')) {
$user = $this->Auth->identify();
if ($user) {
$this->Auth->setUser($user);
debug($this->Auth->User()); //contain user details correctly
debug($this->redirect($this->Auth->redirectUrl())); // //contain userdetails correctly
return $this->redirect($this->Auth->redirectUrl());
}
$this->Flash->error(__('Invalid username or password, try again'));
}
}
public function logout()
{
return $this->redirect($this->Auth->logout());
}
User.php
protected function _setPassword($password)
{
if (strlen($password) > 0) {
return (new DefaultPasswordHasher)->hash($password);
}
}
I print phpinfo() session is enabled. other projects under the "var/www/html" working properly. But inside this project only session not working.