Nette Security: Access Control

Introduction

Authentication & Authorization library for Nette.

user login and logout
verifying user privileges
securing against vulnerabilities
how to create custom authenticators and authorizators
Access Control List

Documentation can be found on the website.

It requires PHP version 8.0 and supports PHP up to 8.2.

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Authentication

Authentication means user login, ie. the process during which a user's identity is verified. The user usually identifies himself using username and password. Verification is performed by the so-called authenticator. If the login fails, it throws Nette\Security\AuthenticationException.

try {
	$user->login($username, $password);
} catch (Nette\Security\AuthenticationException $e) {
	$this->flashMessage('The username or password you entered is incorrect.');
}

Logging him out:

$user->logout();

And checking if user is logged in:

echo $user->isLoggedIn() ? 'yes' : 'no';

Simple, right? And all security aspects are handled by Nette for you.

You can also set the time interval after which the user logs off (otherwise he logs off with session expiration). This is done by the method setExpiration(), which is called before login(). Specify a string with relative time as a parameter:

// login expires after 30 minutes of inactivity
$user->setExpiration('30 minutes');

// cancel expiration
$user->setExpiration(null);

Expiration must be set to value equal or lower than the expiration of sessions.

The reason of the last logout can be obtained by method $user->getLogoutReason(), which returns either the constant Nette\Security\IUserStorage::INACTIVITY if the time expired or IUserStorage::MANUAL when the logout() method was called.

In presenters, you can verify login in the startup() method:

protected function startup()
{
	parent::startup();
	if (!$this->getUser()->isLoggedIn()) {
		$this->redirect('Sign:in');
	}
}

Authenticator

It is an object that verifies the login data, ie usually the name and password. The trivial implementation is the class Nette\Security\SimpleAuthenticator, which can be defined this way

$authenticator = new Nette\Security\SimpleAuthenticator([
	# name => password
	'johndoe' => 'secret123',
	'kathy' => 'evenmoresecretpassword',
]);

This solution is more suitable for testing purposes. We will show you how to create an authenticator that will verify credentials against a database table.

An authenticator is an object that implements the Nette\Security\IAuthenticator interface with method authenticate(). Its task is either to return the so-called identity or to throw an exception Nette\Security\AuthenticationException. It would also be possible to provide an fine-grain error code IAuthenticator::IDENTITY_NOT_FOUND or IAuthenticator::INVALID_CREDENTIAL.

use Nette;

class MyAuthenticator implements Nette\Security\IAuthenticator
{
	private $database;
	private $passwords;

	public function __construct(Nette\Database\Context $database, Nette\Security\Passwords $passwords)
	{
		$this->database = $database;
		$this->passwords = $passwords;
	}

	public function authenticate(array $credentials): Nette\Security\IIdentity
	{
		[$username, $password] = $credentials;

		$row = $this->database->table('users')
			->where('username', $username)
			->fetch();

		if (!$row) {
			throw new Nette\Security\AuthenticationException('User not found.');
		}

		if (!$this->passwords->verify($password, $row->password)) {
			throw new Nette\Security\AuthenticationException('Invalid password.');
		}

		return new Nette\Security\Identity(
			$row->id,
			$row->role, // or array of roles
			['name' => $row->username]
		);
	}
}

The MyAuthenticator class communicates with the database through Nette Database Explorer and works with table users, where column username contains the user's login name and column password contains hash. After verifying the name and password, it returns the identity with user's ID, role (column role in the table), which we will mention later , and an array with additional data (in our case, the username).

$onLoggedIn, $onLoggedOut events

Object Nette\Security\User has events $onLoggedIn and $onLoggedOut, so you can add callbacks that are triggered after a successful login or after the user logs out.

$user->onLoggedIn[] = function () {
	// user has just logged in
};

Identity

An identity is a set of information about a user that is returned by the authenticator and which is then stored in a session and retrieved using $user->getIdentity(). So we can get the id, roles and other user data as we passed them in the authenticator:

$user->getIdentity()->getId();
// also works shortcut $user->getId();

$user->getIdentity()->getRoles();

// user data can be access as properties
// the name we passed on in MyAuthenticator
$user->getIdentity()->name;

Importantly, when user logs out, identity is not deleted and is still available. So, if identity exists, it by itself does not grant that the user is also logged in. If we want to explicitly delete the identity, we logout the user by $user->logout(true).

Thanks to this, you can still assume which user is at the computer and, for example, display personalized offers in the e-shop, however, you can only display his personal data after logging in.

Identity is an object that implements the Nette\Security\IIdentity interface, the default implementation is Nette\Security\Identity. And as mentioned, identity is stored in the session, so if, for example, we change the role of some of the logged-in users, old data will be kept in the identity until he logs in again.

Authorization

Authorization determines whether a user has sufficient privileges, for example, to access a specific resource or to perform an action. Authorization assumes previous successful authentication, ie that the user is logged in.

For very simple websites with administration, where user rights are not distinguished, it is possible to use the already known method as an authorization criterion isLoggedIn(). In other words: once a user is logged in, he has permissions to all actions and vice versa.

if ($user->isLoggedIn()) { // is user logged in?
	deleteItem(); // if so, he may delete an item
}

Roles

The purpose of roles is to offer a more precise permission management and remain independent on the user name. As soon as user logs in, he is assigned one or more roles. Roles themselves may be simple strings, for example, admin, member, guest, etc. They are specified in the second argument of Identity constructor, either as a string or an array.

As an authorization criterion, we will now use the method isInRole(), which checks whether the user is in the given role:

if ($user->isInRole('admin')) { // is the admin role assigned to the user?
	deleteItem(); // if so, he may delete an item
}

As you already know, logging the user out does not erase his identity. Thus, method getIdentity() still returns object Identity, including all granted roles. The Nette Framework adheres to the principle of "less code, more security", so when you are checking roles, you do not have to check whether the user is logged in too. Method isInRole() works with effective roles, ie if the user is logged in, roles assigned to identity are used, if he is not logged in, an automatic special role guest is used instead.

Authorizator

In addition to roles, we will introduce the terms resource and operation:

role is a user attribute - for example moderator, editor, visitor, registered user, administrator, ...
resource is a logical unit of the application - article, page, user, menu item, poll, presenter, ...
operation is a specific activity, which user may or may not do with resource - view, edit, delete, vote, ...

An authorizer is an object that decides whether a given role has permission to perform a certain operation with specific resource. It is an object implementing the Nette\Security\IAuthorizator interface with only one method isAllowed():

class MyAuthorizator implements Nette\Security\IAuthorizator
{
	public function isAllowed($role, $resource, $operation): bool
	{
		if ($role === 'admin') {
			return true;
		}
		if ($role === 'user' && $resource === 'article') {
			return true;
		}

		...

		return false;
	}
}

And the following is an example of use. Note that this time we call the method Nette\Security\User::isAllowed(), not the authorizator's one, so there is not first parameter $role. This method calls MyAuthorizator::isAllowed() sequentially for all user roles and returns true if at least one of them has permission.

if ($user->isAllowed('file')) { // is user allowed to do everything with resource 'file'?
	useFile();
}

if ($user->isAllowed('file', 'delete')) { // is user allowed to delete a resource 'file'?
	deleteFile();
}

Both arguments are optional and their default value means everything.

Permission ACL

Nette comes with a built-in implementation of the authorizer, the Nette\Security\Permission class, which offers a lightweight and flexible ACL (Access Control List) layer for permission and access control. When we work with this class, we define roles, resources, and individual permissions. And roles and resources may form hierarchies. To explain, we will show an example of a web application:

guest: visitor that is not logged in, allowed to read and browse public part of the web, ie. read articles, comment and vote in polls
registered: logged-in user, which may on top of that post comments
administrator: can manage articles, comments and polls

So we have defined certain roles (guest, registered and administrator) and mentioned resources (article, comments, poll), which the users may access or take actions on (view, vote, add, edit).

We create an instance of the Permission class and define roles. It is possible to use the inheritance of roles, which ensures that, for example, a user with a role administrator can do what an ordinary website visitor can do (and of course more).

$acl = new Nette\Security\Permission;

$acl->addRole('guest');
$acl->addRole('registered', 'guest'); // registered inherits from guest
$acl->addRole('administrator', 'registered'); // and administrator inherits from registered

We will now define a list of resources that users can access:

$acl->addResource('article');
$acl->addResource('comment');
$acl->addResource('poll');

Resources can also use inheritance, for example, we can add $acl->addResource('perex', 'article').

And now the most important thing. We will define between them rules determining who can do what:

// everything is denied now

// let the guest view articles, comments and polls
$acl->allow('guest', ['article', 'comment', 'poll'], 'view');
// and also vote in polls
$acl->allow('guest', 'poll', 'vote');

// the registered inherits the permissions from guesta, we will also let him to comment
$acl->allow('registered', 'comment', 'add');

// the administrator can view and edit anything
$acl->allow('administrator', $acl::All, ['view', 'edit', 'add']);

What if we want to prevent someone from accessing a resource?

// administrator cannot edit polls, that would be undemocractic.
$acl->deny('administrator', 'poll', 'edit');

Now when we have created the set of rules, we may simply ask the authorization queries:

// can guest view articles?
$acl->isAllowed('guest', 'article', 'view'); // true

// can guest edit an article?
$acl->isAllowed('guest', 'article', 'edit'); // false

// can guest vote in polls?
$acl->isAllowed('guest', 'poll', 'vote'); // true

// may guest add comments?
$acl->isAllowed('guest', 'comment', 'add'); // false

The same applies to a registered user, but he can also comment:

$acl->isAllowed('registered', 'article', 'view'); // true
$acl->isAllowed('registered', 'comment', 'add'); // true
$acl->isAllowed('registered', 'comment', 'edit'); // false

The administrator can edit everything except polls:

$acl->isAllowed('administrator', 'poll', 'vote'); // true
$acl->isAllowed('administrator', 'poll', 'edit'); // false
$acl->isAllowed('administrator', 'comment', 'edit'); // true

Permissions can also be evaluated dynamically and we can leave the decision to our own callback, to which all parameters are passed:

$assertion = function (Permission $acl, string $role, string $resource, string $privilege): bool {
	return ...;
};

$acl->allow('registered', 'comment', null, $assertion);

But how to solve a situation where the names of roles and resources are not enough, ie we would like to define that, for example, a role registered can edit a resource article only if it is its author? We will use objects instead of strings, the role will be the object Nette\Security\IRole and the source Nette\Security\IResource. Their methods getRoleId() resp. getResourceId() will return the original strings:

class Registered implements Nette\Security\IRole
{
	public $id;

	public function getRoleId(): string
	{
		return 'registered';
	}
}


class Article implements Nette\Security\IResource
{
	public $authorId;

	public function getResourceId(): string
	{
		return 'article';
	}
}

And now let's create a rule:

$assertion = function (Permission $acl, string $role, string $resource, string $privilege): bool {
	$role = $acl->getQueriedRole(); // object Registered
	$resource = $acl->getQueriedResource(); // object Article
	return $role->id === $resource->authorId;
};

$acl->allow('registered', 'article', 'edit', $assertion);

The ACL is queried by passing objects:

$user = new Registered(...);
$article = new Article(...);
$acl->isAllowed($user, $article, 'edit');

A role may inherit form one or more other roles. But what happens, if one ancestor has certain action allowed and the other one has it denied? Then the role weight comes into play - the last role in the array of roles to inherit has the greatest weight, first one the lowest:

$acl = new Nette\Security\Permission;
$acl->addRole('admin');
$acl->addRole('guest');

$acl->addResource('backend');

$acl->allow('admin', 'backend');
$acl->deny('guest', 'backend');

// example A: role admin has lower weight than role guest
$acl->addRole('john', ['admin', 'guest']);
$acl->isAllowed('john', 'backend'); // false

// example B: role admin has greater weight than role guest
$acl->addRole('mary', ['guest', 'admin']);
$acl->isAllowed('mary', 'backend'); // true

Roles and resources can also be removed (removeRole(), removeResource()), rules can also be reverted (removeAllow(), removeDeny()). The array of all direct parent roles returns getRoleParents(). Whether two entities inherit from each other returns roleInheritsFrom() and resourceInheritsFrom().

Multiple Independent Authentications

It is possible to have several independent logged users within one site and one session at a time. For example, if we want to have separate authentication for frontend and backend, we will just set a unique session namespace for each of them:

$user->getStorage()->setNamespace('forum');

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