Callback Verification

Some verification operations cannot be performed well on RDBMS servers. Other times, you may be unsure which RDBMS system you will be using long-term, and need to ensure authentication will work consistently. For these situations, you can use the Zend\Authentication\Adapter\DbTable\CallbackCheckAdapter adapter. Similar to the CredentialTreatmentAdapter, it accepts a table name, identity column, and credential column; however, instead of a credential treatment, it accepts a credential validation callback that is executed when the database returns any matches, and which can be used to perform additional credential verifications.

Configuration options

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.
  • credentialValidationCallback: A PHP callable to execute when the database returns matches. The callback will receive:
  • the value of the credentialColumn returned from the database
  • the credential that was used by the adapter during authentication

Basic Usage

Many databases do not provide functions that implement a cryptographically secure hashing mechanism. Additionally, you may want to ensure that should you switch database systems, hashing is consistent. This is a perfect use case for the CallbackCheckAdapter adapter; you can implement the password hashing and verification within PHP instead.

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:

use Zend\Db\Adapter\Adapter as DbAdapter;

// Create a SQLite database connection
$dbAdapter = new DbAdapter([
    'driver'   => 'Pdo_Sqlite',
    'database' => 'data/sqlite.db',

// Build a simple table creation query
$sqlCreate = 'CREATE TABLE [users] ('
    . '[username] VARCHAR(50) UNIQUE NOT NULL, '
    . '[password] VARCHAR(255) NULL, '
    . '[real_name] VARCHAR(150) NULL)';

// Create the authentication credentials table

// 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

As you add users, you will need to create a hash of the password provided and insert that into the database. For users on PHP 5.5+, you can use password_hash():

$hash = password_hash($password, PASSWORD_DEFAULT);

Password hash length

As of the time of writing, PHP uses a bcrypt algorithm by default for hashing passwords with password_hash(), and this produces 60 character strings. However, the default may change over time, and recommends using 255 character fields for storage to allow for larger hash sizes in the future.

To verify a password, we'll create a callback that uses password_verify():

$passwordValidation = function ($hash, $password) {
    return password_verify($password, $hash);

Now that we have the database connection and a password validation function, we can create our Zend\Authentication\Adapter\DbTable\CallbackCheckAdapter adapter instance, passing the options to the constructor or later via setter methods:

use Zend\Authentication\Adapter\DbTable\CallbackCheckAdapter as AuthAdapter;

// Configure the instance with constructor parameters:
$authAdapter = new AuthAdapter(

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


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:

// Set the input credential values (e.g., from a login form):

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

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

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

// Print the result row:

/* Output:

    [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:

// Specify the columns to return:
$columnsToReturn = [

/* Output:

   [id] => 1
   [username] => my_username
   [real_name] => My Real Name

// Or specify the columns to omit; when using this approach,
// pass a null value as the first argument to getResultRowObject():
$columnsToOmit = ['password'];
print_r($authAdapter->getResultRowObject(null, $columnsToOmit);

/* Output:

   [id] => 1
   [username] => my_username
   [real_name] => My Real Name

Advanced Usage

While the basic use case will fit most scenarios, there may be cases where you have specialized needs, such as additional criteria that needs to be met for a user to match.

Adding criteria to match

Since the validation callback is only provided the hash value from the database and the credential provided by the user, you cannot do more complex matching within it. However, you can add criteria to the SQL sent to the server by retrieving the Zend\Db\Sql\Select instance is uses.

As an example, many websites require a user to activate their account before allowing them to login for the first time. We can add that criteria as follows:

// Create a basic adapter, with only an MD5() credential treatment:
$adapter = new AuthAdapter(

// Now retrieve the Select instance and modify it:
$select = $adapter->getDbSelect();
$select->where('active = "TRUE"');

// Authenticate; this will include " = TRUE" in the WHERE clause:

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