Hi Volker
You could use your customizing table as encrypted ones and decripting them at runtime
Check out Encryption Algorithm using class :CL_HARD_WIRED_ENCRYPTOR
and the suggested links in replies at this thread
How to encrypt and decrypt data in Abap
You can create as first step a report that read USer and password (like a web registration form), entrcypt what you want and then store to a table.
In your connection, read table, decrypt and use.