[Samba] Password policy under Samba 4?

[Michael Wood]

How does one set a password policy using Samba 4?

I've set up Samba 4 as a domain controller with one Windows 2003
server joined to the domain.  I've seen mention of the "check password
script" option, but I think that's not available in Samba 4, right?
I've also seen mention of Group Policies, but I am not sure if this is
correct or not because I haven't been able to find anything in the
Group Policy management tool on Windows that seems applicable.

Basically I just want to know where to set the "user must change
password after 30 days" and "password must be at least X characters
long" settings and have these apply to users logging into the Windows
machine.

I'd appreciate it if someone could point me at the relevant documentation.

-- 
Michael Wood <esiotrot at gmail.com>