krb5_get_userdn
krb5_get_userdn(krb5_context, krb5_db_entry *, char **);
((st=krb5_get_userdn(context, entry, &(DN))) != 0))
st = krb5_get_userdn(context, entry, &dn);
((st=krb5_get_userdn(context, entry, &principal_dn)) != 0))