Being a mere mortal I would like to refer to a very interesting point that I fully agree with. It's expressed by a person well respected in Oracle and beyond. I am sure you know/heard of him - http://tkyte.blogspot.com/2005/05/why.html
From your post it was quite clear that what you do doesn't make much sence (or read it as not clear at all what is the purpose) and, consequently, mix of incompatible methods of athentication. The question about initial requirements and ideas is very appropriate in this context and I hinted that very clearly. Perhaps, you have read this already but it might be useful to get back to it and others might find it very interesting as well - http://www.catb.org/~esr/faqs/smart-questions.html#goal
To summarize, with no replies on your question for two hours I wanted to be helpful enough to hint you possible directions instead of simple RTFM that some people consider to be a bit rude (well, I don't!). In case of any concerns, please contact me privately and I am very open to discuss it.
You know, I don't understand what is it with some experts that when you ask a question - that you have looked everywhere to find the answer and you couldn't or you could but didn't understand it - instead of helping you, make you more confused by asking other questions like "why do you want to do this?".
Maybe I'm not an expert in Oracle. But if I was I would never answer somebody's question like that.
Thanks again Jared, Amir
-- Best regards, Alex Gorbachev