Show message for end user on errors with LDAP server in Plone

gistfile1.py

patches.py:
from plone.api.portal import show_message
from cStringIO import StringIO
import logging

fake_log_file = StringIO()
aux_logger = logging.StreamHandler(fake_log_file)
aux_logger.setLevel(logging.ERROR)
ldap_logger = logging.getLogger('event.LDAPDelegate')
ldap_logger.addHandler(aux_logger)

msg = "Something went wrong while connecting to the LDAP server(s)"


def authenticateCredentials(self, credentials):
    fake_log_file.truncate(0)  # empty log to catch only current messages
    try:
        self._old_authenticateCredentials(credentials)
    except:
        raise
    finally:
        if fake_log_file.getvalue():
            # Assume something went wrong if it is logged.
            show_message(msg, self.REQUEST, type='error')
    return None, None


configure.zcml:
<monkey:patch
    description="Show message on LDAP errors."
    class="Products.LDAPMultiPlugins.LDAPPluginBase.LDAPPluginBase"
    original="authenticateCredentials"
    replacement=".patches.authenticateCredentials"
    preserveOriginal="true"
/>