simonm pointed out my first thought when I read this node - I have different items restricted to different pipes. CC numbers need to come in over the web, but not go out over the web. They need to go out to the CC provider, but not come in from that pipe. And, they may have to go back and forth over the DB connection.

But, the DB user/password@sid should never go anywhere except to the database. (It shouldn't come back from the database, even.)

I don't think this is really useful, as it stands. It also sounds like it's something that should be done at the application level, not at the language or OS level.