CORS issue when using zipkin endpoint with opentelemetry-js

[nagarajatantry]

Describe the Bug

I am experimenting with opentelemetry-js in the web with zipkin endpoint. It seems to send x-opentelemetry-outgoing-request in the header causing CORS issue.

Steps to Reproduce

• Run zipkin locally
  • Base example --> https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/tracer-web
  • Add Zipkin related changes

  • 
    import { ZipkinExporter } from "@opentelemetry/exporter-zipkin";
    provider.addSpanProcessor(new SimpleSpanProcessor(new ZipkinExporter({
       serviceName:"document-load"
       url: "http://localhost:9411/v2/spans"
    })));

[codefromthecrypt]

I don't have access to transfer this to the https://github.com/open-telemetry/opentelemetry-js repo which is where it should go. We have no control over that library, nor the choices of headers it chooses to send. I have no idea what x-opentelemetry-outgoing-request is, but I doublt it is intended to send to zipkin: you should open an issue to ensure it isn't or there's a solid explanation of why.

That said, the primary problem I suspect is the incorrect, missing the "api" part http://localhost:9411/api/v2/spans

[vmarchaud]

I've opened an issue on our end to fix that https://github.com/open-telemetry/opentelemetry-js/issues/983