Gitlab CI job with specific user - docker

Question

I am trying to run Gitlab CI job of anchore engine to scan docker image. The command in script section fails with error of permission denied. I found out the command requires root user permissions. Sudo is not installed in the docker image I'm using as gitlab runner and only non sudo user anchore is there in the docker container.
Below is the CI job for container scanning.
container_scan:
stage: scan
image:
name: anchore/anchore-engine:latest
entrypoint: ['']
services:
- name: anchore/engine-db-preload:latest
alias: anchore-db
variables:
GIT_STRATEGY: none
ANCHORE_HOST_ID: "localhost"
ANCHORE_ENDPOINT_HOSTNAME: "localhost"
ANCHORE_CLI_USER: "admin"
ANCHORE_CLI_PASS: "foobar"
ANCHORE_CLI_SSL_VERIFY: "n"
ANCHORE_FAIL_ON_POLICY: "true"
ANCHORE_TIMEOUT: "500"
script:
- |
curl -o /tmp/anchore_ci_tools.py https://raw.githubusercontent.com/anchore/ci-tools/master/scripts/anchore_ci_tools.py
chmod +x /tmp/anchore_ci_tools.py
ln -s /tmp/anchore_ci_tools.py /usr/local/bin/anchore_ci_tools
- anchore_ci_tools --setup
- anchore-cli registry add "$CI_REGISTRY" gitlab-ci-token "$CI_JOB_TOKEN" --skip-validate
- anchore_ci_tools --analyze --report --image "$IMAGE_NAME" --timeout "$ANCHORE_TIMEOUT"
- |
if ; then
anchore-cli evaluate check "$IMAGE_NAME"
else
set +o pipefail
anchore-cli evaluate check "$IMAGE_NAME" | tee /dev/null
fi
artifacts:
name: ${CI_JOB_NAME}-${CI_COMMIT_REF_NAME}
paths:
- image-*-report.json
The CI job fails at ln -s /tmp/anchore_ci_tools.py /usr/local/bin/anchore_ci_tools in the script section.
I have tried to add user in the entrypoint section
name: anchore/anchore-engine:latest
entrypoint: ['bash', '-c', 'useradd myuser && exec su myuser -c bash']
but it did not allow to create a user. I have tried running the docker container in linux with docker run -it --user=root anchore/anchore-engine:latest /bin/bash and it run without any problem. How can I simulate the same in gitlab-ci job?