Chainable authentication adapters in Zend Framework

AdapterChain.php

<?php
namespace My\Authentication\Adapter;

use Zend\Authentication\Adapter\AbstractAdapter;
use Zend\Authentication\Adapter\Exception\InvalidArgumentException;
use Zend\Authentication\Adapter\ValidatableAdapterInterface;
use Zend\Authentication\Result;

class AdapterChain extends AbstractAdapter
{

    private $adapters;

    public function __construct(array $adapters)
    {
        if (count($adapters) < 1) {
            throw new InvalidArgumentException('There must be at least one authentication adapter');
        }
        
        foreach ($adapters as $adapter) {
            if (!($adapter instanceof ValidatableAdapterInterface)) {
                throw new InvalidArgumentException('All adapters must implement ValidatableAdapterInterface');
            }
        }
        
        $this->adapters = $adapters;
    }

    public function authenticate()
    {
        if (!$this->identity) {
            return new Result(Result::FAILURE_IDENTITY_NOT_FOUND, '', [
                'A username is required'
            ]);
        }
        
        if (!$this->credential) {
            return new Result(Result::FAILURE_CREDENTIAL_INVALID, '', [
                'A password is required'
            ]);
        }
        
        // try all adapters in the chain
        foreach ($this->adapters as $adapter) {
            $adapter->setIdentity($this->identity);
            $adapter->setCredential($this->credential);
            
            $result = $adapter->authenticate();
            
            // try the next adapter if the identity is not found
            if ($result->getCode() === Result::FAILURE_IDENTITY_NOT_FOUND) {
                continue;
            }
            
            return $result;
        }
    }
}