LDAP can be enabled with sentry,FOR LDAPS you will need ssl key and certificate which is the next step.(For security purposes).
Secondly to enable sentry with hive/impala you need to have an admin user,check in allowed.users property in impala,sentry configurations.
You will get to know which users have the privilege to bypass the sentry authorization so that you can give roles and privileges to other users using an admin user.
Go to impala shell by switching to that admin user.I tried with impala
-->su impala
--->impala-shell
Grant roles and privileges using sql statements .Take a look at this url
http://www.cloudera.com/content/cloudera/en/documentation/core/v5-2-x/topics/sg_hive_sql.html