doSocialLogin.php

private function _doSocialLogin($profile, $returning = false) {

	$user_exist = !empty($profile['SocialProfile']['user_id'])  ? $this->User->findById($profile['SocialProfile']['user_id']) : null;

	if ($user_exist && $user_exist['User']['is_registered'] == 1) {
		if ($user_exist['User']['is_active'] == 1) {
			if ($this->Auth->login($user_exist['User'])) {

				if ($this->Auth->login()) {
					
					// is_logged mantiene constancia de si un usuario tiene sesion abierta o no
					// Update islogged
					$this->loadModel('User');
					$this->User->id = $this->Auth->user('id');
					$this->User->saveField('is_logged', true);

					if ($this->Auth->user('logged') === null) {
						//Chipirones por Registrarse
						$this->Chipirones->addCredit('signin', $this->Auth->user('id'));
						$this->Notifications->notify(1, 'Welcome', 'Welcome To Studentfy!');
						$this->Chipirones->addAchievenment('signin', $this->Auth->user('id'));
						$this->Notifications->notify(2, 'Add Chipirones', 'We give you +100 Chipirones for signing up on our platform!');
						
						// anyadir carrito de compra
						$this->ShoppingCart->createShoppingCart($this->Auth->user('id'));
						$this->loadModel('SharesUser');
						$inv_reg = $this->SharesUser->find('first', [
							'conditions' => [
								'email_of_registration' => $this->Auth->user('email'),
								'registered' => 1,
								'paid' => 0
							]
						]); 

						$this->loadModel('User');
						$this->User->isLogged($this->Auth->user('id'));
						$this->Session->write('NewUser', true); // To know the new user
					}        
					return $this->redirect('/');
				}

			} else {
				$this->Flash->set(__('Unknown Error could not verify the user: '. $this->Auth->user('username')));
				$this->redirect('/');
			}
		} else {
			if ($user_exist['User']['is_active'] == 2) {
				$this->Flash->set(__('Your account has been canceled. Please contact the site administrator.'));

				return $this->redirect('/');
			} else {
				$this->Flash->set(__('Your account has not been verified, '. $user_exist['User']['fullname'] .'. Please contact the site administrator.'));

				return $this->redirect('/');
			}
			
		}
	} else {
		$this->Session->write(
			'userProfile',
			$profile
		);
		$this->redirect(array('controller' => 'accounts', 'action' => 'register'));
	}
}

social_endpoint.php

public function social_endpoint($provider = null) {
	$this->Hybridauth->processEndpoint();
}

social_login.php

// Aqui viene la peticion cuando el usuario le da click a "Logerse con facebook"

public function social_login($provider, $count = 0) {
	$this->isLoggin();
	$this->set([
		'provider' => $provider
	]);
	try {
		if( $this->Hybridauth->connect($provider) ){

			$exist_native = $this->User->find('first',[
				'conditions' => [
					'email' => $this->Hybridauth->user_profile['SocialProfile']['email'],
					'login_type_id' => 1
				]
			]);
			// valida si ya posee registro
			if (empty($exist_native)) {
				$this->_successfulHybridauth($provider,$this->Hybridauth->user_profile);
			}
			else {
				/*$this->Flash->set('The email \''.$this->Hybridauth->user_profile['SocialProfile']['email'].'\' has been registered by native login. Please enter email and password to log in.
If you forget your password, click on the \'forgot password\' link.',['element' => 'error']);*/
				$this->Flash->set('The email \''.$this->Hybridauth->user_profile['SocialProfile']['email'].'\' has been registered by native login. Please enter email and password to log in.
If you forget your password, click on the \'forgot password\' link.',['element' => 'error']);
				$this->redirect($this->Auth->loginAction);
			}
		}
		else{
			// error

			$this->Flash->set($this->Hybridauth->error);
			$this->redirect($this->Auth->loginAction);
		}
	} catch (Exception $e) {
		++ $count;
		if ($count <= 10) {
			$this->Flash->set(__('Failed to connect to provider '. $provider. '. Please try again later.'),['element' => 'error']);
			$this->redirect($this->Auth->loginAction);
		}
		else {
			$this->social_login($provider, $count);
		}
	}
}

successfulHybridauth.php

private function _successfulHybridauth($provider, $incomingProfile){

	// #1 - check if user already authenticated using this provider before
	$this->SocialProfile->recursive = -1;
	$existingProfile = $this->SocialProfile->find('first', array(
		'conditions' => array('social_network_id' => $incomingProfile['SocialProfile']['social_network_id'], 'social_network_name' => $provider)
	));

	if (!empty($existingProfile)) {

		if (empty($existingProfile['SocialProfile']['user_id'])) {
			$this->_doSocialLogin($existingProfile);
		}
		else {
			// #2 - if an existing profile is available, then we set the user as connected and log them in
			$user = $this->User->find('first', array(
				'conditions' => array('id' => $existingProfile['SocialProfile']['user_id'])
			));
			
			if (empty($user)) {
			  // Tiene un user_id asignado pero esta mal
			}

			$this->_doSocialLogin($existingProfile);
		}
	}
	else {
		if ($this->Auth->loggedIn()) {
			$this->redirect($this->Auth->redirectUrl());
		} else {

			if($this->SocialProfile->save($incomingProfile)) {
			  // el perfil se guardo correctamente
			}

			$this->_doSocialLogin($incomingProfile);
		}
	}
}