Kaniko does not use custom HTTP User-Agent when pushing to docker registry

[pitastrudl]

Actual behavior
Using variable UPSTREAM_CLIENT_TYPE: "docker" in gitlab-ci.yaml in Docker-in-docker mode, kaniko does not send the expected user agent with the specified header or appended. What I see in nginx logs os that the User-agent is '"Go-http-client/2.0"'.

Expected behavior
I expect to see User-Agent to be custom defined with the "docker" value or it appended after the default user-agent used.

Additional Information

I use Nexus registry behind nginx reverse proxy. Since the tag is also the hostname of the proxy. I use below if statement in nginx to proxy docker client requests.

              if ($$http_user_agent ~* docker) {
                  proxy_pass $$upstream_docker;
              }

Seems like Kaniko uses normal http requests and I am trying to change the user-agent to a custom one, for it to work. Kaniko is running in Docker-in-docker mode inside gitlab runner. I have not seen any notes on how to do it but searching through the code I found this and unsure if it's intended to be used or if it even works:

kaniko/pkg/executor/push.go

Line 61 in e328007

UpstreamClientUaKey = "UPSTREAM_CLIENT_TYPE"

I did also try adding it into the config.json inside kaniko but it did not work
: - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}},\"HttpHeaders\":{\"User-Agent\":\"Docker-Client/custom-nginx-dind-docker\"}}" > /kaniko/.docker/config.json

I am using the latest gcr.io/kaniko-project/executor:debug debug image v1.23.2.
Kaniko is run with - /kaniko/executor --cache=true --context $CONTEXT --dockerfile $DOCKERFILE_PATH --destination $DOCKER_TAG
The setup is running in docker swarm.

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko	- [ x]
Please check if this error is seen when you use --cache flag	- [x ]
Please check if your dockerfile is a multistage dockerfile