check for password
*back, struct passwd
*pwd, char *class,
function is called by a BSD Authentication login
script to check whether the user's password entry, as described by
pwd, has expired.
If a class is specified, it is used instead of the class specified in the user's password database entry. If the lastchance argument is non-zero, the user's password has expired, and it has not been expired longer than “password-dead” seconds (see login.conf(5)), the user will be able to log in one last time to change the password.
login_check_expire() function returns
0 if the user's password has not expired, and 1 if it has expired or if an
Status and error messages are passed back to the login script caller via the back channel, back.
auth_subr(3), authenticate(3), login.conf(5)