remote password change

[pepe]

I have two FreeBSD 8 servers running. Server A is for shell access and
server B for www pages. On B there is only scp/sftp access and no shell
login.
Now I'm looking for solution for people to be able to change password for
server B from inside server A. Or better yet, automatic migration of
password so if user changes password for server A it would change in server
B too. Are there some solutions to do this?

-- 
pepe