setIdentityColumn example

$credential = $this->_credential;
        $credentialColumn = $this->_credentialColumn;
        $identity = $this->_identity;
        $identityColumn = $this->_identityColumn;
        $credentialTreatment = $this->_credentialTreatment;

        $expiry = Zend_Date::now()->subSecond($this->expiry);
        $this->setCredential($expiry);
        $this->setCredentialColumn($this->expiryColumn);

        $this->setIdentity($this->sessionId);
        $this->setIdentityColumn($this->sessionIdColumn);

        $result = parent::authenticate();

        $this->_credential = $credential;
        $this->_credentialColumn = $credentialColumn;
        $this->_identity = $identity;
        $this->_identityColumn = $identityColumn;
        $this->_credentialTreatment = $credentialTreatment;

        if ($result->isValid()) {
            $this->updateExpiry();
        }

    public function __construct(Zend_Db_Adapter_Abstract $zendDb = null, $tableName = null, $identityColumn = null,
                                $credentialColumn = null, $credentialTreatment = null)
    {
        $this->_setDbAdapter($zendDb);

        if ($tableName !== null) {
            $this->setTableName($tableName);
        }

        if ($identityColumn !== null) {
            $this->setIdentityColumn($identityColumn);
        }

        if ($credentialColumn !== null) {
            $this->setCredentialColumn($credentialColumn);
        }

        if ($credentialTreatment !== null) {
            $this->setCredentialTreatment($credentialTreatment);
        }
    }