User Login Problems

I'm a Oracle/Sybase person moving into Informix and to tell you the truth, logging seems a strange concept to Informix. Here's what I have done in Oracle yet seems impossible to do in Informix: * Each user log-in from a PC into Informix on an HP with their own username and password. * Each user can change their password (or have a privledged DB user do it.) It doesn't seem that a user logged into Unix can log into Informix as a different user. It seems that Informix is lacking and is forcing me into a design where I maintain my own list of users and have everyone log in as the same (secret) username/password. This doesn't seem optimal. Anyway, you have been kind enough to read this much. So does anyone have any thought or solutions to this problem? Thanks in advance, John Dennis Aeronomics, Inc.