Support W3C Baggage proposed standard in HttpHandlerDiagnosticListener

[jbogard]

The W3C Correlation-Context proposed standard was renamed to "baggage". As part of that rename, the header was renamed from Correlation-Context to baggage.

The details of the spec are in public working draft, which remain the same as Correlation-Context except with the header name change.

Since this is a potentially breaking change (server may be expecting the legacy name Correlation-Context, either this can be a clean break (remove/rename Correlation-Context to baggage), or it can be done in phases:

1. Populate both headers with same value
2. Remove legacy header name/value

Related: dotnet/aspnetcore#28319

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[jbogard]

@tommcdon I think this is probably yours, I didn't get the label magic to work. It's System.Diagnostics.DiagnosticSource.

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Issue Details

---

The W3C Correlation-Context proposed standard was renamed to "baggage". As part of that rename, the header was renamed from Correlation-Context to baggage.

The details of the spec are in public working draft, which remain the same as Correlation-Context except with the header name change.

Since this is a potentially breaking change (server may be expecting the legacy name Correlation-Context, either this can be a clean break (remove/rename Correlation-Context to baggage), or it can be done in phases:

1. Populate both headers with same value
2. Remove legacy header name/value

Related: dotnet/aspnetcore#28319

Author:	jbogard
Assignees:	-
Labels:	area-System.Diagnostics.Tracing, untriaged
Milestone:	-

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

The W3C Correlation-Context proposed standard was renamed to "baggage". As part of that rename, the header was renamed from Correlation-Context to baggage.

The details of the spec are in public working draft, which remain the same as Correlation-Context except with the header name change.

Since this is a potentially breaking change (server may be expecting the legacy name Correlation-Context, either this can be a clean break (remove/rename Correlation-Context to baggage), or it can be done in phases:

1. Populate both headers with same value
2. Remove legacy header name/value

Related: dotnet/aspnetcore#28319

Author:	jbogard
Assignees:	-
Labels:	area-System.Net.Http, untriaged
Milestone:	-

[karelz]

Triage: We should do it once the spec is final. Is that the case already @jbogard?
cc @MihaZupan

[jbogard]

No, it is not. It moved into the first public working draft status back on October 20th, 2020. However, the Correlation-Context header behavior for Baggage was implemented before this standard was in public working draft status.

It's in an odd place - the name of the standard/header was renamed, and now in public working draft, but it was the "old" name, never standardized, that was implemented for .NET Core 3.0.

[karelz]

Oh, does it mean that we implemented a draft, that won't be part of the final spec?
We can either act right away, or wait for the spec to mature a bit more ... @MihaZupan what would you recommend?
Either way, we will have to deal with handling potential breaking change for customers -- are there mitigations we can put in place? (e.g. generating both headers)