linux servlet -> /etc/passwd authentication

[Allen Harper]

I am playing with trying to get a tomcat servlet to get username and
password from a user and authenticate with the underlying linux
/etc/passwd /etc/shadow file.  I have looked into JAAS, it only seems to
support NT, database, and flat text file authentication.  From what I
can tell, it may not exist.  Have you seen anything on this or have any
ideas of how to make it work? 
 
If I have to, I will turn off shadowing for this application...
 
Examples of code would be greatly appreciated.
 
allen