Access private git repos via npm install in a Docker container

I am in the process of setting up a Docker container that will pull private repos from GitHub as part of the process. At the moment I am using an Access Token that I pass from the command line (will change once build gets triggered via Jenkins).

docker build -t my-container --build-arg GITHUB_API_TOKEN=123456 .

# Dockerfile
# Env Vars
ARG GITHUB_API_TOKEN
ENV GITHUB_API_TOKEN=${GITHUB_API_TOKEN}

RUN git clone https://${GITHUB_API_TOKEN}@github.com/org/my-repo

This works fine and seems to be a secure way of doing this? (though need to check the var GITHUB_API_TOKEN only being available at build time)

I am looking to find out how people deal with ssh keys or access tokens when running npm install and dependencies pull from github

"devDependencies": {
  "my-repo": "git@github.com:org/my-repo.git",
  "electron": "^1.7.4"
}

At the moment I cannot pull this repo as I get the error Please make sure you have the correct access rights as I have no ssh keys setup in this container