It's just a question of what you want.
If you do keepalive with authentication, you are able to verify that the HTTP server is alive and that the server is able to do authentication.
So the server is fully operational.
If you only do HTTP keepalive, you can only verify that the server is alive.
If for some reason the server is unable to authentication users, being alive is not enough to function properly.
The only advantage of not doing http authentication with keepalive it's because it is easier.
Our HTTP kal script with authentication is limited to NTLM.
If you do something else, you don't even have the choice.
Regards,
Gilles.
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