>>The only implementations of the PAM framework that I know about are
>>commercial (Sun, HP, ...)  and GPL (Linux).

and BSD license (freebsd).

>Linux PAM is dual licensed, and frankly a very small amount of code
>anyway.

And likely not necessary anyway.  I've not looked at every single module
in freebsd's pam, but all the ones I've looked at have a BSD license
as does the core libpam library.  In fact a grep of all the .c files (169)
under freebsd's libpam shows only one (pam_krb5.c) that mentions 
a GNU license.

--sjg