class ZC_Auth_Adapter
    implements Zend_Auth_Adapter_Interface
{
    const NOT_FOUND_MSG = "Account not found";
    const BAD_PW_MSG    = "Password is invalid";

    protected $user;

    protected $username = "";
    protected $password = "";

    public function  __construct($username, $password)
    {
        $this->username = $username;
        $this->password = $password;
    }

    public function authenticate()
    {
        try
        {
            $this->user = Model_User::authenticate($this->username, $this->password);
            return $this->createResult(Zend_Auth_Result::SUCCESS);
        } catch (Exception $e) {
            if($e->getMessage() == Model_User::WRONG_PASSWORD)
                    return $this->createResult(Zend_Auth_Result::FAILURE_CREDENTIAL_INVALID, array(self::BAD_PW_MSG));

            if($e->getMessage() == Model_User::NOT_FOUND)
                    return $this->createResult(Zend_Auth_Result::FAILURE_IDENTITY_NOT_FOUND, array(self::NOT_FOUND_MSG));
        }
    }

    private function createResult($code, $messages = array())
    {
        return new Zend_Auth_Result($code, $this->user, $messages);
    }
}