Hi Thiago,
Fortunately we are currently involved with LDAP heavil on both Active Directory and OpenLDAP as the providers - both of which Pentaho security successfully integrated with - so I can share a bit.
For the BI Server (web portal) part, I will leave it to be answered by my colleague at PHI who is more technically competent.
In the ETL part, you can just use the LDAP Input / Output step. All you need is to specify the host, port, authenticated user, DN, and attributes that existed in the LDAP provider you are using.
The following screenshot is our design to reset password of all LDAP users as a part of "data cleansing".
Hope it helps a bit though is not a walkthrough tutorial :)
Regards,
Feris