If you need the user's password in plaintext (or something easily derived from it), then your authentication scheme shouldn't send it over the network at all: there are better ways to handle that scenario.

Also keep in mind that a machine storing plaintext passwords has the same security requirements as a Kerberos KDC, and those requirements are very, very high. Don't do this unless you know what you're doing, and even if you do, you should seriously consider a different scheme (or just using Kerberos itself: they've already gotten things right, so you don't have to risk getting things wrong).

You should almost never know a users plaintext password. Outside of a small set of scenarios you're likely doing something very wrong if you need a users plaintext passwords. Passwords should almost always be bcrypt'd.