.. _zend.authentication.introduction:

Introduction
============

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 :ref:`Zend\\Permissions\\Acl <zend.permissions.acl>` 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.

.. _zend.authentication.introduction.adapters:

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:

.. code-block:: php
   :linenos:

   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``.

.. _zend.authentication.introduction.results:

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:

.. code-block:: php
   :linenos:

   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:

.. code-block:: php
   :linenos:

   // 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;
   }

.. _zend.authentication.introduction.persistence:

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.

.. _zend.authentication.introduction.persistence.default:

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 :ref:`Zend\\Session <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 forego using the ``Zend\Authentication\AuthenticationService`` class altogether, instead using an adapter
   class directly.

.. _zend.authentication.introduction.persistence.default.example:

.. rubric:: 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 :ref:`Zend\\Session\\Container <zend.session>`. This should
occur before authentication is attempted, since ``Zend\Authentication\AuthenticationService::authenticate()``
performs the automatic storage of the identity.

.. code-block:: php
   :linenos:

   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);

.. _zend.authentication.introduction.persistence.custom:

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()``.

.. _zend.authentication.introduction.persistence.custom.example:

.. rubric:: 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``:

.. code-block:: php
   :linenos:

   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:

.. code-block:: php
   :linenos:

   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);

.. _zend.authentication.introduction.using:

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:

.. code-block:: php
   :linenos:

   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:

.. code-block:: php
   :linenos:

   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:

.. code-block:: php
   :linenos:

   $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``:

.. code-block:: php
   :linenos:

   // 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
   }