Virtual Host External authentication

I have successfully setup the server and it works flawless. However I have run into a problem

How do i configure one of the virtual hosts to use and external authentication script without affecting the other
virtual hosts. this is what i have in the authentication section

%%% ==============
%%% AUTHENTICATION

%%
%% auth_method: Method used to authenticate the users.
%% The default method is the internal.
%% If you want to use a different method,
%% comment this line and enable the correct ones.
%%
{auth_method, internal}.

%%
%% Authentication using external script
%% Make sure the script is executable by ejabberd.
%%
%%{auth_method, external}.
%%{extauth_program, "/path/to/authentication/script"}.

%%
%% Authentication using ODBC
%% Remember to setup a database in the next section.
%%
%%{auth_method, odbc}.

%%
%% Authentication using PAM
%%
%%{auth_method, pam}.
%%{pam_service, "pamservicename"}.

%%
%% Authentication using LDAP
%%
%%{auth_method, ldap}.
%%
%% List of LDAP servers:
%%{ldap_servers, ["server.virtualhost.com"]}.
%%
%% LDAP attribute that holds user ID:
%%{ldap_uids, [{"mail", "%u@mail.example.org"}]}.
%%
%% Search base of LDAP directory:
%%{ldap_base, "dc=example,dc=com"}.
%%
%% LDAP manager:
%%{ldap_rootdn, "dc=example,dc=com"}.
%%
%% Password to LDAP manager:
%%{ldap_password, "******"}.

%%
%% Anonymous login support:
%% auth_method: anonymous
%% anonymous_protocol: sasl_anon | login_anon | both
%% allow_multiple_connections: true | false
%%
%%{host_config, "public.example.org", [{auth_method, anonymous},
%% {allow_multiple_connections, false},
%% {anonymous_protocol, sasl_anon}]}.
%%
%% To use both anonymous and internal authentication:
%%
%%{host_config, "public.example.org", [{auth_method, [internal, anonymous]}]}.
{host_config, "virtualhost2.com",[{auth_method, external}]}.
{extauth_program, "php /opt/ejabberd-2.0.5/auth/ssc_ext_auth.php"}.

at the top it has auth_method internal and the bottom i have the host config for the second host as external
Do I need to define all virtual hosts or will the auto internal at the top control all others

Thanks in advance