Introduction to Zend\Authentication

The Zend\Authentication component provides an API for authentication and includes concrete authentication adapters for common use case scenarios.

Zend\Authentication is concerned only with authentication and not with authorization. Authentication is loosely defined as determining whether an entity actually is what it purports to be (i.e., identification), based on some set of credentials. Authorization, the process of deciding whether to allow an entity access to, or to perform operations upon, other entities is outside the scope of Zend\Authentication. For more information about authorization and access control with Zend Framework, please see the Zend\Permissions\Acl or Zend\Permissions\Rbac component.

Note

There is no Zend\Authentication\Authentication class, instead the class Zend\Authentication\AuthenticationService is provided. This class uses underlying authentication adapters and persistent storage backends.

Adapters

Zend\Authentication adapters are used to authenticate against a particular type of authentication service, such as LDAP, RDBMS, or file-based storage. Different adapters are likely to have vastly different options and behaviors, but some basic things are common among authentication adapters. For example, accepting authentication credentials (including a purported identity), performing queries against the authentication service, and returning results are common to Zend\Authentication adapters.

Each Zend\Authentication adapter class implements Zend\Authentication\Adapter\AdapterInterface. This interface defines one method, authenticate(), that an adapter class must implement for performing an authentication query. Each adapter class must be prepared prior to calling authenticate(). Such adapter preparation includes setting up credentials (e.g., username and password) and defining values for adapter-specific configuration options, such as database connection settings for a database table adapter.

The following is an example authentication adapter that requires a username and password to be set for authentication. Other details, such as how the authentication service is queried, have been omitted for brevity:

use Zend\Authentication\Adapter\AdapterInterface;

class My\Auth\Adapter implements AdapterInterface
{
    /**
     * Sets username and password for authentication
     *
     * @return void
     */
    public function __construct($username, $password)
    {
        // ...
    }

    /**
     * Performs an authentication attempt
     *
     * @return \Zend\Authentication\Result
     * @throws \Zend\Authentication\Adapter\Exception\ExceptionInterface
     *               If authentication cannot be performed
     */
    public function authenticate()
    {
        // ...
    }
}

As indicated in its docblock, authenticate() must return an instance of Zend\Authentication\Result (or of a class derived from Zend\Authentication\Result). If for some reason performing an authentication query is impossible, authenticate() should throw an exception that derives from Zend\Authentication\Adapter\Exception\ExceptionInterface.

Results

Zend\Authentication adapters return an instance of Zend\Authentication\Result with authenticate() in order to represent the results of an authentication attempt. Adapters populate the Zend\Authentication\Result object upon construction, so that the following four methods provide a basic set of user-facing operations that are common to the results of Zend\Authentication adapters:

• isValid()- returns TRUE if and only if the result represents a successful authentication attempt
• getCode()- returns a Zend\Authentication\Result constant identifier for determining the type of authentication failure or whether success has occurred. This may be used in situations where the developer wishes to distinguish among several authentication result types. This allows developers to maintain detailed authentication result statistics, for example. Another use of this feature is to provide specific, customized messages to users for usability reasons, though developers are encouraged to consider the risks of providing such detailed reasons to users, instead of a general authentication failure message. For more information, see the notes below.
• getIdentity()- returns the identity of the authentication attempt
• getMessages()- returns an array of messages regarding a failed authentication attempt

A developer may wish to branch based on the type of authentication result in order to perform more specific operations. Some operations developers might find useful are locking accounts after too many unsuccessful password attempts, flagging an IP address after too many nonexistent identities are attempted, and providing specific, customized authentication result messages to the user. The following result codes are available:

use Zend\Authentication\Result;

Result::SUCCESS
Result::FAILURE
Result::FAILURE_IDENTITY_NOT_FOUND
Result::FAILURE_IDENTITY_AMBIGUOUS
Result::FAILURE_CREDENTIAL_INVALID
Result::FAILURE_UNCATEGORIZED

The following example illustrates how a developer may branch on the result code:

// inside of AuthController / loginAction
$result = $this->auth->authenticate($adapter);

switch ($result->getCode()) {

    case Result::FAILURE_IDENTITY_NOT_FOUND:
        /** do stuff for nonexistent identity **/
        break;

    case Result::FAILURE_CREDENTIAL_INVALID:
        /** do stuff for invalid credential **/
        break;

    case Result::SUCCESS:
        /** do stuff for successful authentication **/
        break;

    default:
        /** do stuff for other failure **/
        break;
}

Identity Persistence

Authenticating a request that includes authentication credentials is useful per se, but it is also important to support maintaining the authenticated identity without having to present the authentication credentials with each request.

HTTP is a stateless protocol, however, and techniques such as cookies and sessions have been developed in order to facilitate maintaining state across multiple requests in server-side web applications.

Default Persistence in the PHP Session

By default, Zend\Authentication provides persistent storage of the identity from a successful authentication attempt using the PHP session. Upon a successful authentication attempt, Zend\Authentication\AuthenticationService::authenticate() stores the identity from the authentication result into persistent storage. Unless specified otherwise, Zend\Authentication\AuthenticationService uses a storage class named Zend\Authentication\Storage\Session, which, in turn, uses Zend\Session. A custom class may instead be used by providing an object that implements Zend\Authentication\Storage\StorageInterface to Zend\Authentication\AuthenticationService::setStorage().

Note

If automatic persistent storage of the identity is not appropriate for a particular use case, then developers may forget using the Zend\Authentication\AuthenticationService class altogether, instead using an adapter class directly.

Modifying the Session Namespace

Zend\Authentication\Storage\Session uses a session namespace of ‘Zend_Auth‘. This namespace may be overridden by passing a different value to the constructor of Zend\Authentication\Storage\Session, and this value is internally passed along to the constructor of Zend\Session\Container. This should occur before authentication is attempted, since Zend\Authentication\AuthenticationService::authenticate() performs the automatic storage of the identity.

use Zend\Authentication\AuthenticationService;
use Zend\Authentication\Storage\Session as SessionStorage;

$auth = new AuthenticationService();

// Use 'someNamespace' instead of 'Zend_Auth'
$auth->setStorage(new SessionStorage('someNamespace'));

/**
 * @todo Set up the auth adapter, $authAdapter
 */

// Authenticate, saving the result, and persisting the identity on
// success
$result = $auth->authenticate($authAdapter);

Chain Storage

A website may have multiple storage in place. The Chain Storage can be used to glue these together.

The Chain can for example be configured to first use a Session Storage and then use a OAuth as a secondary Storage. One could configure this in the following way:

 $storage = new Chain;
 $storage->add(new Session);
 $storage->add(new OAuth); // Note: imaginary storage, not part of ZF2

Now if the Chain Storage is accessed its underlying Storage will get accessed in the order in which they were added to the chain. Thus first the Session Storage is used. Now either:

• The Session Storage is non-empty and the Chain will use its contents.
• The Sesssion Storage is empty. Next the OAuth Storage is accessed.
  • If this one is also empty the Chain will act as empty.
  • If this one is non-empty the Chain will use its contents. However it will also populate all Storage with higher priority. Thus the Session Storage will be populated with the contents of the Oauth Storage.

The priority of Storage in the Chain can be made explicit via the Chain::add method.

 $chain->add(new A, 2);
 $chain->add(new B, 10); // First use B

Implementing Customized Storage

Sometimes developers may need to use a different identity storage mechanism than that provided by Zend\Authentication\Storage\Session. For such cases developers may simply implement Zend\Authentication\Storage\StorageInterface and supply an instance of the class to Zend\Authentication\AuthenticationService::setStorage().

Using a Custom Storage Class

In order to use an identity persistence storage class other than Zend\Authentication\Storage\Session, a developer implements Zend\Authentication\Storage\StorageInterface:

use Zend\Authentication\Storage\StorageInterface;

class My\Storage implements StorageInterface
{
    /**
     * Returns true if and only if storage is empty
     *
     * @throws \Zend\Authentication\Exception\ExceptionInterface
     *               If it is impossible to
     *               determine whether storage is empty
     * @return boolean
     */
    public function isEmpty()
    {
        /**
         * @todo implementation
         */
    }

    /**
     * Returns the contents of storage
     *
     * Behavior is undefined when storage is empty.
     *
     * @throws \Zend\Authentication\Exception\ExceptionInterface
     *               If reading contents from storage is impossible
     * @return mixed
     */

    public function read()
    {
        /**
         * @todo implementation
         */
    }

    /**
     * Writes $contents to storage
     *
     * @param  mixed $contents
     * @throws \Zend\Authentication\Exception\ExceptionInterface
     *               If writing $contents to storage is impossible
     * @return void
     */

    public function write($contents)
    {
        /**
         * @todo implementation
         */
    }

    /**
     * Clears contents from storage
     *
     * @throws \Zend\Authentication\Exception\ExceptionInterface
     *               If clearing contents from storage is impossible
     * @return void
     */

    public function clear()
    {
        /**
         * @todo implementation
         */
    }
}

In order to use this custom storage class, Zend\Authentication\AuthenticationService::setStorage() is invoked before an authentication query is attempted:

use Zend\Authentication\AuthenticationService;

// Instruct AuthenticationService to use the custom storage class
$auth = new AuthenticationService();

$auth->setStorage(new My\Storage());

/**
 * @todo Set up the auth adapter, $authAdapter
 */

// Authenticate, saving the result, and persisting the identity on
// success
$result = $auth->authenticate($authAdapter);

Usage

There are two provided ways to use Zend\Authentication adapters:

• indirectly, through Zend\Authentication\AuthenticationService::authenticate()
• directly, through the adapter’s authenticate() method

The following example illustrates how to use a Zend\Authentication adapter indirectly, through the use of the Zend\Authentication\AuthenticationService class:

use Zend\Authentication\AuthenticationService;

// instantiate the authentication service
$auth = new AuthenticationService();

// Set up the authentication adapter
$authAdapter = new My\Auth\Adapter($username, $password);

// Attempt authentication, saving the result
$result = $auth->authenticate($authAdapter);

if (!$result->isValid()) {
    // Authentication failed; print the reasons why
    foreach ($result->getMessages() as $message) {
        echo "$message\n";
    }
} else {
    // Authentication succeeded; the identity ($username) is stored
    // in the session
    // $result->getIdentity() === $auth->getIdentity()
    // $result->getIdentity() === $username
}

Once authentication has been attempted in a request, as in the above example, it is a simple matter to check whether a successfully authenticated identity exists:

use Zend\Authentication\AuthenticationService;

$auth = new AuthenticationService();

/**
 * @todo Set up the auth adapter, $authAdapter
 */

if ($auth->hasIdentity()) {
    // Identity exists; get it
    $identity = $auth->getIdentity();
}

To remove an identity from persistent storage, simply use the clearIdentity() method. This typically would be used for implementing an application “logout” operation:

$auth->clearIdentity();

When the automatic use of persistent storage is inappropriate for a particular use case, a developer may simply bypass the use of the Zend\Authentication\AuthenticationService class, using an adapter class directly. Direct use of an adapter class involves configuring and preparing an adapter object and then calling its authenticate() method. Adapter-specific details are discussed in the documentation for each adapter. The following example directly utilizes My\Auth\Adapter:

// Set up the authentication adapter
$authAdapter = new My\Auth\Adapter($username, $password);

// Attempt authentication, saving the result
$result = $authAdapter->authenticate();

if (!$result->isValid()) {
    // Authentication failed; print the reasons why
    foreach ($result->getMessages() as $message) {
        echo "$message\n";
    }
} else {
    // Authentication succeeded
    // $result->getIdentity() === $username
}