Add support for flowing the Activity/distributed trace context via SignalR invocations

[davidfowl]

We need to make a provision in the SignalR hub protocol for flowing the distributed trace context. This will enable causality tracking across multiple SignalR applications or from an HTTP server calling a SignalR method. It's also worth thinking about what it means to flow the context back to the client for server -> client invocations.

[analogrelay]

If we expanded Hub Pipeline to work on the client as well, this could probably be done in that.

[davidfowl]

@anurse it also needs to be done client side.

@SergeyKanzhelev We should have a quick sync about this.

[ghost]

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. Because it's not immediately obvious that this is a bug in our framework, we would like to keep this around to collect more feedback, which can later help us determine the impact of it. 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.

[davidfowl]

We have headers in messages, we could finally use them here @BrennanConroy. It'll end up allocating async locals though...

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[alexdresko]

Ha. I just spent a lot of time getting my .NET 6 application in my k8s cluster to post its metrics and traces through otelcol to jaeger, only to find out that the SignalR integration just isn't there. That's pretty disappointing from where I sit right now, so I'm leaving a comment to remind people that this is an important issue. :)

[phaza]

For everyone else who struggles with this, there's work in progress here to fix this: #46164