A Zend_Auth adapter is 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_Auth adapters.

Each Zend_Auth adapter class implements Zend_Auth_Adapter_Interface. 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:

class MyAuthAdapter implements Zend_Auth_Adapter_Interface
{
    /**
     * Sets username and password for authentication
     *
     * @return void
     */
    public function __construct($username, $password)
    {
        // ...
    }

    /**
     * Performs an authentication attempt
     *
     * @throws Zend_Auth_Adapter_Exception If authentication cannot
     *                                     be performed
     * @return Zend_Auth_Result
     */
    public function authenticate()
    {
        // ...
    }
}

As indicated in its docblock, authenticate() must return an instance of Zend_Auth_Result (or of a class derived from Zend_Auth_Result). If for some reason performing an authentication query is impossible, authenticate() should throw an exception that derives from Zend_Auth_Adapter_Exception.

Zend_Auth adapters return an instance of Zend_Auth_Result with authenticate() in order to represent the results of an authentication attempt. Adapters populate the Zend_Auth_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_Auth adapters:

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:

Zend_Auth_Result::SUCCESS
Zend_Auth_Result::FAILURE
Zend_Auth_Result::FAILURE_IDENTITY_NOT_FOUND
Zend_Auth_Result::FAILURE_IDENTITY_AMBIGUOUS
Zend_Auth_Result::FAILURE_CREDENTIAL_INVALID
Zend_Auth_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 Zend_Auth_Result::FAILURE_IDENTITY_NOT_FOUND:
        /** do stuff for nonexistent identity **/
        break;

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

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

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

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.

// Save a reference to the Singleton instance of Zend_Auth
$auth = Zend_Auth::getInstance();

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

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

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

class MyStorage implements Zend_Auth_Storage_Interface
{
    /**
     * Returns true if and only if storage is empty
     *
     * @throws Zend_Auth_Storage_Exception 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_Auth_Storage_Exception If reading contents from
     *                                     storage is impossible
     * @return mixed
     */
    public function read()
    {
        /**
         * @todo implementation
         */
    }

    /**
     * Writes $contents to storage
     *
     * @param  mixed $contents
     * @throws Zend_Auth_Storage_Exception If writing $contents to
     *                                     storage is impossible
     * @return void
     */
    public function write($contents)
    {
        /**
         * @todo implementation
         */
    }

    /**
     * Clears contents from storage
     *
     * @throws Zend_Auth_Storage_Exception If clearing contents from
     *                                     storage is impossible
     * @return void
     */
    public function clear()
    {
        /**
         * @todo implementation
         */
    }
}

// Instruct Zend_Auth to use the custom storage class
Zend_Auth::getInstance()->setStorage(new MyStorage());

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

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

There are two provided ways to use Zend_Auth adapters:

The following example illustrates how to use a Zend_Auth adapter indirectly, through the use of the Zend_Auth class:

// Get a reference to the singleton instance of Zend_Auth
$auth = Zend_Auth::getInstance();

// Set up the authentication adapter
$authAdapter = new MyAuthAdapter($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:

$auth = Zend_Auth::getInstance();
if ($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:

Zend_Auth::getInstance()->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_Auth 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 MyAuthAdapter:

// Set up the authentication adapter
$authAdapter = new MyAuthAdapter($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
}