[carey]

At least when it was released, IIS 10 supported HTTP/2, but did not support Kerberos, Negotiate or NTLM authentication over HTTP/2.

https://docs.microsoft.com/en-us/iis/get-started/whats-new-i...

I’m not sure that it’s a problem with HTTP/2 that Microsoft found no reason to implement Windows authentication for it.

[jiggawatts]

The HTTP/2 protocol specifically makes this kind of authentication difficult. It's not just IIS, in general it doesn't quite work right.