Mapping LDAP groups to portal roles

Hi,

We are already using LDAP as datasource for users and currently assign roles to the users in the portal.

To optimize the process we are trying to add portal roles to the LDAP group, so that portal access can be assigned to the users just by adding them to the group in LDAP.

We were able to add the roles to the group but the users in the group not getting the access.

Tried looking for any standard documents but couldn't find any.

Can somebody please guide me through the process.

Thanks in advance.