bridge/opentracing: propagated baggage item key is canonicalized

[scorpionknifes]

Description

When a baggage item key is added to a bridge span, they shouldn't be canonicalized by http.CanonicalHeaderKey

opentelemetry-go/bridge/opentracing/bridge.go

Lines 76 to 88 in 1cfd83a

	func (c *bridgeSpanContext) setBaggageItem(restrictedKey, value string) {
	crk := http.CanonicalHeaderKey(restrictedKey)
	m, err := baggage.NewMember(crk, value)
	if err != nil {
	return
	}
	c.bag, _ = c.bag.SetMember(m)
	}
	func (c *bridgeSpanContext) baggageItem(restrictedKey string) baggage.Member {
	crk := http.CanonicalHeaderKey(restrictedKey)
	return c.bag.Member(crk)
	}

Baggage keys are case sensitive, they are not supposed to be mangled this way --
https://github.com/w3c/baggage/blob/ebda53c1d33031d95f1104f44840d3d4b875eb89/baggage/HTTP_HEADER_FORMAT_RATIONALE.md?plain=1#L55
Originally posted by @yurishkuro in #4776 (comment)

Additional Info
Seems like this was added in the initial opentracing bridge implementation in https://www.github.com/open-telemetry/opentelemetry-go/issues/98

opentelemetry-java does not canonicalize the keys: https://github.com/open-telemetry/opentelemetry-java/blob/227580ba0956fcd43429d684b7e0798c8723481a/opentracing-shim/src/main/java/io/opentelemetry/opentracingshim/SpanShim.java#L166-L188

opentelemetry-dotnet also does not canonicalize the key: https://github.com/open-telemetry/opentelemetry-dotnet/blob/0889e8dc32badbb4c9be8fd24a974fb7e61fa779/src/OpenTelemetry.Shims.OpenTracing/SpanShim.cs#L140-L144

There aren't any references to canonicalizing in spec: https://opentelemetry.io/docs/specs/otel/compatibility/opentracing/#set-baggage-item

Environment

• OS: macOS
• Architecture: arm
• Go Version: 1.21
• opentelemetry-go version: v1.21.0

Steps To Reproduce

Test from #4776
https://github.com/scorpionknifes/opentelemetry-go/blob/a112d3f67926fe27a2948a8b15380d5c5ccdcbe1/bridge/opentracing/bridge_test.go#L603-L614

Expected behavior

The baggage item key should be the same.