Database Table Authentication

Introduction

Zend\Authentication\Adapter\DbTable provides the ability to authenticate against credentials stored in a database table. Because Zend\Authentication\Adapter\DbTable requires an instance of Zend\Db\Adapter\Adapter to be passed to its constructor, each instance is bound to a particular database connection. Other configuration options may be set through the constructor and through instance methods, one for each option.

The available configuration options include:

  • tableName: This is the name of the database table that contains the authentication credentials, and against which the database authentication query is performed.
  • identityColumn: This is the name of the database table column used to represent the identity. The identity column must contain unique values, such as a username or e-mail address.
  • credentialColumn: This is the name of the database table column used to represent the credential. Under a simple identity and password authentication scheme, the credential value corresponds to the password. See also the credentialTreatment option.
  • credentialTreatment: In many cases, passwords and other sensitive data are encrypted, hashed, encoded, obscured, salted or otherwise treated through some function or algorithm. By specifying a parameterized treatment string with this method, such as ‘MD5(?)‘ or ‘PASSWORD(?)‘, a developer may apply such arbitrary SQL upon input credential data. Since these functions are specific to the underlying RDBMS, check the database manual for the availability of such functions for your database system.

Basic Usage

As explained in the introduction, the Zend\Authentication\Adapter\DbTable constructor requires an instance of Zend\Db\Adapter\Adapter that serves as the database connection to which the authentication adapter instance is bound. First, the database connection should be created.

The following code creates an adapter for an in-memory database, creates a simple table schema, and inserts a row against which we can perform an authentication query later. This example requires the PDO SQLite extension to be available:

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use Zend\Db\Adapter\Adapter as DbAdapter;

// Create a SQLite database connection
$dbAdapter = new DbAdapter(array(
                'driver' => 'Pdo_Sqlite',
                'database' => 'path/to/sqlite.db'
            ));

// Build a simple table creation query
$sqlCreate = 'CREATE TABLE [users] ('
           . '[id] INTEGER  NOT NULL PRIMARY KEY, '
           . '[username] VARCHAR(50) UNIQUE NOT NULL, '
           . '[password] VARCHAR(32) NULL, '
           . '[real_name] VARCHAR(150) NULL)';

// Create the authentication credentials table
$dbAdapter->query($sqlCreate);

// Build a query to insert a row for which authentication may succeed
$sqlInsert = "INSERT INTO users (username, password, real_name) "
           . "VALUES ('my_username', 'my_password', 'My Real Name')";

// Insert the data
$dbAdapter->query($sqlInsert);

With the database connection and table data available, an instance of Zend\Authentication\Adapter\DbTable may be created. Configuration option values may be passed to the constructor or deferred as parameters to setter methods after instantiation:

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use Zend\Authentication\Adapter\DbTable as AuthAdapter;

// Configure the instance with constructor parameters...
$authAdapter = new AuthAdapter($dbAdapter,
                               'users',
                               'username',
                               'password'
                               );

// ...or configure the instance with setter methods
$authAdapter = new AuthAdapter($dbAdapter);

$authAdapter
    ->setTableName('users')
    ->setIdentityColumn('username')
    ->setCredentialColumn('password')
;

At this point, the authentication adapter instance is ready to accept authentication queries. In order to formulate an authentication query, the input credential values are passed to the adapter prior to calling the authenticate() method:

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// Set the input credential values (e.g., from a login form)
$authAdapter
    ->setIdentity('my_username')
    ->setCredential('my_password')
;

// Perform the authentication query, saving the result

In addition to the availability of the getIdentity() method upon the authentication result object, Zend\Authentication\Adapter\DbTable also supports retrieving the table row upon authentication success:

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// Print the identity
echo $result->getIdentity() . "\n\n";

// Print the result row
print_r($authAdapter->getResultRowObject());

/* Output:
my_username

Array
(
    [id] => 1
    [username] => my_username
    [password] => my_password
    [real_name] => My Real Name
)
*/

Since the table row contains the credential value, it is important to secure the values against unintended access.

When retrieving the result object, we can either specify what columns to return, or what columns to omit:

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$columnsToReturn = array(
    'id', 'username', 'real_name'
);
print_r($authAdapter->getResultRowObject($columnsToReturn));

/* Output:

Array
(
   [id] => 1
   [username] => my_username
   [real_name] => My Real Name
)
*/

$columnsToOmit = array('password');
print_r($authAdapter->getResultRowObject(null, $columnsToOmit);

/* Output:

Array
(
   [id] => 1
   [username] => my_username
   [real_name] => My Real Name
)
*/

Advanced Usage: Persisting a DbTable Result Object

By default, Zend\Authentication\Adapter\DbTable returns the identity supplied back to the auth object upon successful authentication. Another use case scenario, where developers want to store to the persistent storage mechanism of Zend\Authentication an identity object containing other useful information, is solved by using the getResultRowObject() method to return a stdClass object. The following code snippet illustrates its use:

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// authenticate with Zend\Authentication\Adapter\DbTable
$result = $this->_auth->authenticate($adapter);

if ($result->isValid()) {
    // store the identity as an object where only the username and
    // real_name have been returned
    $storage = $this->_auth->getStorage();
    $storage->write($adapter->getResultRowObject(array(
        'username',
        'real_name',
    )));

    // store the identity as an object where the password column has
    // been omitted
    $storage->write($adapter->getResultRowObject(
        null,
        'password'
    ));

    /* ... */

} else {

    /* ... */

}

Advanced Usage By Example

While the primary purpose of the Zend\Authentication component (and consequently Zend\Authentication\Adapter\DbTable) is primarily authentication and not authorization, there are a few instances and problems that toe the line between which domain they fit within. Depending on how you’ve decided to explain your problem, it sometimes makes sense to solve what could look like an authorization problem within the authentication adapter.

With that disclaimer out of the way, Zend\Authentication\Adapter\DbTable has some built in mechanisms that can be leveraged for additional checks at authentication time to solve some common user problems.

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use Zend\Authentication\Adapter\DbTable as AuthAdapter;

// The status field value of an account is not equal to "compromised"
$adapter = new AuthAdapter($db,
                           'users',
                           'username',
                           'password',
                           'MD5(?) AND status != "compromised"'
                           );

// The active field value of an account is equal to "TRUE"
$adapter = new AuthAdapter($db,
                           'users',
                           'username',
                           'password',
                           'MD5(?) AND active = "TRUE"'
                           );

Another scenario can be the implementation of a salting mechanism. Salting is a term referring to a technique which can highly improve your application’s security. It’s based on the idea that concatenating a random string to every password makes it impossible to accomplish a successful brute force attack on the database using pre-computed hash values from a dictionary.

Therefore, we need to modify our table to store our salt string:

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$sqlAlter = "ALTER TABLE [users] "
          . "ADD COLUMN [password_salt] "
          . "AFTER [password]";

Here’s a simple way to generate a salt string for every user at registration:

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$dynamicSalt = '';
for ($i = 0; $i < 50; $i++) {
    $dynamicSalt .= chr(rand(33, 126));
}

And now let’s build the adapter:

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$adapter = new AuthAdapter($db,
                           'users',
                           'username',
                           'password',
                           "MD5(CONCAT('staticSalt', ?, password_salt))"
                          );

Note

You can improve security even more by using a static salt value hard coded into your application. In the case that your database is compromised (e. g. by an SQL injection attack) but your web server is intact your data is still unusable for the attacker.

Another alternative is to use the getDbSelect() method of the Zend\Authentication\Adapter\DbTable after the adapter has been constructed. This method will return the Zend\Db\Sql\Select object instance it will use to complete the authenticate() routine. It is important to note that this method will always return the same object regardless if authenticate() has been called or not. This object will not have any of the identity or credential information in it as those values are placed into the select object at authenticate() time.

An example of a situation where one might want to use the getDbSelect() method would check the status of a user, in other words to see if that user’s account is enabled.

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// Continuing with the example from above
$adapter = new AuthAdapter($db,
                           'users',
                           'username',
                           'password',
                           'MD5(?)'
                           );

// get select object (by reference)
$select = $adapter->getDbSelect();
$select->where('active = "TRUE"');

// authenticate, this ensures that users.active = TRUE
$adapter->authenticate();

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