/**
* Returns true if and only if $value meets the validation requirements
*
* If $value fails validation, then this method returns false, and
* getMessages() will return an array of messages that explain why the
* validation failed.
*
* @param mixed $value
* @param mixed $content
* @return boolean
* @throws \Zend_Validate_Exception If validation of $value is impossible
*/
public function isValid($value, $context = array())
{
$result = $this->_user->authenticate($value);
return $this->setAuthResult($result);
}