Unable to login with a SQL Authenticator

For a project, we are migrating Forms to ADF.
There is also a number of reports which are not to be migrated yet.
Therefore, we need to keep the users in the database.
As we do not want to maintain two user stores, we thought it to be a good idea to create an authenticator in WebLogic to authenticate to the database.
There are loads of blog posts / support notes on how to configure (more...)