Testing that a website is using Kerberos authentication

Question

How do you go about checking that an IIS website is successfully using Kerberos and not falling back on NTLM?

Answer 1

One way I found to test in code that you are using Kerberos is that that the HTTP_AUTHORIZATION header for NTLM always starts with the following:

Negotiate TlRMTVNTUA

If the header doesn't start with text then the browser is authenticating using Kerberos.