I have $auth_allow_default = 1; so guests can view a record designated by a link on another page. This works fine. However, accessing the ADMIN or any valid login to modify accounts, etc seems to be only available if I change the value back to zero.

Is there a way to log in via URL as ADMIN or other accounts?

Pertinent attributes follows:
$auth_no_authentication = 1;
$auth_time = 21600;
$auth_logging = 1;
$auth_allow_default = 1;
@auth_default_permissions = (1,0,0,0,0);
$auth_signup = 0;
@auth_signup_permissions = (1,0,0,0,0);
$auth_modify_own = 0;
$auth_view_own = 0;
$auth_user_field = -1;