Kerberos auth for SemEHR endpoints

[jas88]

Kerberos ("Integrated") auth for the API would be valuable for the HIC deployment, to avoid the need to maintain another set of passwords. EPCC/NSH deployment relies on network-level isolation for this, so little or no authentication is needed there, but HIC is another story.

There's a Nuget package which should handle most of the heavy lifting for us:
https://github.com/dotnet/Kerberos.NET/tree/develop/Samples/KerberosMiddlewareEndToEndSample