On Ubuntu 16.06 (daily build 23/02/2016), the interface is not the same as in gnome-system-tools, but one can see that
the file src/users/run-passwd.c present in gnome-system-tools
was reused in panels/user-accounts/run-passwd.c in ubuntu-control-center
with some modifications. maybe it can help
On Ubuntu 16.06 (daily build 23/02/2016), the interface is not the same as in gnome-system-tools, but one can see that run-passwd. c present in gnome-system-tools user-accounts/ run-passwd. c in ubuntu- control- center
the file src/users/
was reused in panels/
with some modifications. maybe it can help