Hi,
I was able to resolve the issue.
I was not specifying correct parameters in Plugins.properties file.
There was no problem with Parameters. We can use the normal query as it is. i.e
attr.First\ Name = OU=Users,OU=Standard Users:(mailNickName=$endpoint-user-name$):givenName
Regarding log files, you can find out the log file (for Linux) at
/var/log/Vontu/tomcat/localhost.<date>.log
Thanks a lot.