Use object indirection in HttpContextAccessor (#1066)

[JunTaoLuo]

Addresses #5144. This is backporting 49d785c to 2.2

[Tratcher]

Note the branches aren't opening for a few weeks.

[JunTaoLuo]

Description:

In 2.2 we made a change to require request's TraceIdentifier to match when retrieving the HttpContext from the HttpContextAccessor. The goal of the change was to reduce the chance of an invalid HttpContext from being retrieved once the request has ended. However, this caused a regression since if any middleware modifies the TraceIdentifier on the request, the HttpContextAccessor will return a null value for HttpContext. In 3.0 a different approach is used to mitigate the retrieval of invalid HttpContext without relying on the TraceIdentifier. As a side-effect, the regression in behaviour was also removed.

Customer Impact

As mentioned in #5144, any customers on 2.2 will not be able to retrieve HttpContext from HttpContextAccessor if they modify the TraceIdentifier of the request.

Regression?

Regression from 2.1.

Risk:

Low. The fix has already been made to 3.0, we are just backporting it to 2.2

[davidfowl]

We should add a regression test for that case we missed.

[vivmishra]

Approved for 2.2.2.
Wait for branch to open.

[dougbu]

Before merging, please update the 2.2.2 section of eng/PatchConfig.props: https://github.com/aspnet/Extensions/blob/d8407116d183debaadb801c0cbc41d65927999d6/eng/PatchConfig.props#L7-L10