User management
Users can be managed using the UserManager which is injected from the ServerContainer:
<?php
namespace OCA\MyApp\AppInfo;
use \OCP\AppFramework\App;
use \OCA\MyApp\Service\UserService;
class Application extends App {
    public function __construct(array $urlParams=array()){
        parent::__construct('myapp', $urlParams);
        $container = $this->getContainer();
        /**
         * Controllers
         */
        $container->registerService('UserService', function($c) {
            return new UserService(
                $c->query('UserManager')
            );
        });
        $container->registerService('UserManager', function($c) {
            return $c->query('ServerContainer')->getUserManager();
        });
    }
}
Creating users
Creating a user is done by passing a username and password to the create method:
<?php
namespace OCA\MyApp\Service;
class UserService {
    private $userManager;
    public function __construct($userManager){
        $this->userManager = $userManager;
    }
    public function create($userId, $password) {
        return $this->userManager->create($userId, $password);
    }
}
Modifying users
Users can be modified by getting a user by the userId or by a search pattern. The returned user objects can then be used to:
- Delete them 
- Set a new password 
- Disable/Enable them 
- Get their home directory 
<?php
namespace OCA\MyApp\Service;
class UserService {
    private $userManager;
    public function __construct($userManager){
        $this->userManager = $userManager;
    }
    public function delete($userId) {
        return $this->userManager->get($userId)->delete();
    }
    // recoveryPassword is used for the encryption app to recover the keys
    public function setPassword($userId, $password, $recoveryPassword) {
        return $this->userManager->get($userId)->setPassword($password, $recoveryPassword);
    }
    public function disable($userId) {
        return $this->userManager->get($userId)->setEnabled(false);
    }
    public function getHome($userId) {
        return $this->userManager->get($userId)->getHome();
    }
}
User session information
To login, logout or getting the currently logged in user, the UserSession has to be injected from the ServerContainer:
<?php
namespace OCA\MyApp\AppInfo;
use \OCP\AppFramework\App;
use \OCA\MyApp\Service\UserService;
class Application extends App {
    public function __construct(array $urlParams=array()){
        parent::__construct('myapp', $urlParams);
        $container = $this->getContainer();
        /**
         * Controllers
         */
        $container->registerService('UserService', function($c) {
            return new UserService(
                $c->query('UserSession')
            );
        });
        $container->registerService('UserSession', function($c) {
            return $c->query('ServerContainer')->getUserSession();
        });
        // currently logged in user, userId can be gotten by calling the
        // getUID() method on it
        $container->registerService('User', function($c) {
            return $c->query('UserSession')->getUser();
        });
    }
}
Then users can be logged in by using:
<?php
namespace OCA\MyApp\Service;
class UserService {
    private $userSession;
    public function __construct($userSession){
        $this->userSession = $userSession;
    }
    public function login($userId, $password) {
        return $this->userSession->login($userId, $password);
    }
    public function logout() {
        $this->userSession->logout();
    }
}