Identity Persistence

Authenticating a request that includes authentication credentials is useful, but it is also often useful to persist the authenticated identity between requests, so the user does not need to provide credentials with each request.

HTTP is a stateless protocol; however, 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 PHP session facilities. 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 depends on zend-session.

You may also implement Zend\Authentication\Storage\StorageInterface, and provide your implementation to Zend\Authentication\AuthenticationService::setStorage().

Bypass the AuthenticationService

If automatic persistent storage of the identity is not appropriate for your use case, you can skip usage of Zend\Authentication\AuthenticationService altogether, and instead use an adapter directly.

Modifying the Session Namespace

Zend\Authentication\Storage\Session uses the session namespace 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() injects the authenticated identity into the configured storage.

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'));

// Set up the auth adapter, $authAdapter
$authAdapter = /* ... */;

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

Chain Storage

A website might use multiple storage strategies for identity persistence; the Chain Storage can be used to glue these together.

For example, the Chain can be configured to first use Session storage and then use an OAuth storage adapter. 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 zend-authentication

When the Chain Storage is used, its underlying storage adapters will be consulted in the order in which they were added to the chain. Using our scenario above, the Session storage adapter will be consulted first. When that happens:

• If the Session storage is non-empty, the Chain will use and return its contents.
• If the Session storage is empty, the Chain will move on to the OAuth storage adapter.
• If the OAuth storage is empty, the Chain will return an empty result.
• If the OAuth storage is non-empty, the Chain will use and return its contents. However, it will also populate all storage adapters with higher priority with the contents; in our example, the Session storage will be populated, but if we'd added any adapters after the OAuth adapter, they would not.

The priority of storage adapters in the Chain can be made explicit via the Chain::add method, which accepts a second argument indicating the priority. (Per standard priority queue usage, higher values have higher priority, and lower or negative values have lower priority.)

$chain->add(new A, 2);
$chain->add(new B, 10); // B will be used first

Implementing Custom Storage

Sometimes developers may need to use a different identity storage mechanism than that provided by Zend\Authentication\Storage\Session. To do so, implement Zend\Authentication\Storage\StorageInterface and supply an instance of your implementation to Zend\Authentication\AuthenticationService::setStorage().

The following examples demonstrate the process.

First, implement Zend\Authentication\Storage\StorageInterface:

<?php
namespace My;

use Zend\Authentication\Storage\StorageInterface;

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

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

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

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

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

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

    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 My\Storage;
use Zend\Authentication\AuthenticationService;

// Create the authentication service instance:
$auth = new AuthenticationService();

// Instruct the authentication service to use the custom storage class:
$auth->setStorage(new Storage());

// Create the authentication adapter:
$adapter = /* ... */;

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