title: Repeat username/password authentication with each call to web service
body: <p>I am creating a web service to expose to my mobile apps.  I currently am implementing a token based authentication solution (because that what I have done in the past); however, I am struggling in this context to understand why I do not simply pass the username and password each time?  I can maintain the password in RAM while running the Mobile app (encrypted between usages if we want to get overly complicated) and then pass it each time I connect to the server and repeat the hash verification each time.  Of course everything is SSL so there is no more risk in terms of network transfer in doing it each time versus do it once is there?  The only CON I see is that the hash validation process might me more expensive than a token validation - maybe.  Are there other cons I am missing here? </p>