foreach_principal
foreach_principal("*", do_check_entry, "check", NULL);
ret = foreach_principal(argv[i], do_cpw_entry, "cpw", &data);
ret = foreach_principal(argv[i], do_del_entry, "del", NULL);
ret = foreach_principal(argv[i], do_ext_keytab, "ext", &data);
ret = foreach_principal(argv[i], do_list_entry, funcname, NULL);
ret = foreach_principal(argv[i], do_get_entry, name, &data);
foreach_principal(const char *, int (*)(krb5_principal, void*),
ret = foreach_principal(argv[i], do_mod_entry, "mod", opt);