I am not hitting an LDAP server directly and am instead using an LDAP proxy that gives us HA to our LDAP servers. Due to the way this software works, I must use posix attributes. With my current configuration, the users in the group I am syncing appear to be syncing properly as I see them in Ambari when logged in as the default admin user, however I cannot login using my AD credentials and get the message "Unable to sign in. Invalid username/password combination." in the Ambari UI.