Support QueryContextAttributes SECPKG_ATTR_NAMES

Would be great to support `SECPKG_ATTR_NAMES` with [QueryContextAttributesW](https://learn.microsoft.com/en-us/windows/win32/api/sspi/nf-sspi-querycontextattributesw) to retrieve the client principal name from the authentication context. This is mostly just a helpful function to easily debug/log the username of the other end.