App proxy bug with Server Sent Events

[gaetansnl]

Description

What happened:

I proxied and app "Argo Workflow", it uses Server Sent Events but the proxy isn't working

 Error copying upstream response Body: context canceled forward/fwd.go:202
2021-09-24T09:15:23Z ERRO [APP:SERVI] "app:service2021/09/24 09:15:23 http: superfluous response.WriteHeader call from github.com/gravitational/oxy/utils.(*StdHandler).ServeHTTP (handler.go:29)\n" utils/cli.go:341
2021-09-29T13:40:17Z             ERRO Error forwarding to /api/v1/stream/applications?resourceVersion=10265237&fields=result.type%2Cresult.application.metadata.name%2Cresult.application.metadata.annotations%2Cresult.application.metadata.labels%2Cresult.application.metadata.creationTimestamp%2Cresult.application.metadata.deletionTimestamp%2Cresult.application.spec%2Cresult.application.operation.sync%2Cresult.application.status.sync.status%2Cresult.application.status.health%2Cresult.application.status.operationState.phase%2Cresult.application.status.operationState.operation.sync%2Cresult.application.status.summary&selector=, err: context canceled forward/fwd.go:17

Reproduction Steps

As minimally and precisely as possible, describe step-by-step how to reproduce the problem.

1. Proxy an app using Server Sent Events

Server Details

• Teleport version (run teleport version): 7.1.2
• Where are you running Teleport? (e.g. AWS, GCP, Dedicated Hardware): AWS

[gaetansnl]

Fixed by #8385