Update negotiate auth to replace reflection with new public API

[JamesNK]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

The current reflection approach is brittle and not trim-friendly: dotnet/runtime#29270 (comment)

Describe the solution you'd like

1. Replace with new API: Implement NegotiateAuthentication API runtime#70720
2. Remove trim warnings from negotiate auth

Additional context

No response

Thanks for contacting us.

We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.