Basic auth very slow

[nestle2377]

Hi, I'm using the basic alternative authentication when the user is not in domain but the authentication is very slow (about 2 minutes)

the domain authentication is very fast.

I've notice in the event viewer on the AD side that the authentication is done 3 times (in this 2 minutes) and only after the last authentication on the client i can access the resource.
I've try to work on GssapiBasicAuthMech but the only that works is krb5 (always in 2 minutes).
in the keytab file I've only one encryption method.

Any suggestion?

this is my location:

      <Location /dominio>
               AuthType GSSAPI
               AuthName "GSSAPI Single Sign On Login"
               GssapiBasicAuth On
               GssapiBasicAuthMech krb5
               #GssapiAllowedMech krb5
               GssapiUseSessions On
               GssapiNegotiateOnce On
               GssapiLocalName On
               GssapiSessionKey key:<RANDOM>
               Session On
               SessionCookieName gssapi_session path=/dominio;domain=red.it;httponly;secure;
               #AuthzSendForbiddenOnFailure On
               #GssapiCredStore keytab:/etc/kerberosRedHat.keytab
               GssapiCredStore keytab:/etc/kerb3.keytab
               Require valid-user
               RewriteEngine on
               RewriteCond %{REMOTE_USER} (.*)
               RewriteRule .* - [E=X_REMOTE_USER:%1]
               RequestHeader set SM_USER %{X_REMOTE_USER}e
       </Location>

thanks!