How to use private repositories as npm git dependencies on Github Actions

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I’m advocate of automatization, and that includes not only CI/CD pipelines, but also I wanted to do it for documentation publishing. Mafalda is split in a lot of packages (currently more than 30!), so I wanted to have a single place where to publish the documentation of all of them. Github Pages allows to host a website for your organization or username by free (this blog and personal site already makes use of it), and it can also host automatically a website for each repository as sub-paths of your username/organization main website. Problem is, that it only works for open source repositories or for paid plans, and most of the Mafalda SFU repositories are private ones. So since the Mafalda SFU project website is already hosted on Github Pages as a public repository, I decided to store and serve from it all the other repositories documentation as well… doing it in an automated way :-)

The task can be splitted in two halves: generate the documentation, and publish it.


This is the Github Actions workflow I’m using to tests the different Mafalda SFU sub-projects, generate their documentation, and publish it to the Mafalda SFU project website:

name: test, build documentation and publish

    branches: [ main ]
    branches: [ main ]

    runs-on: ubuntu-latest
      - uses: actions/checkout@v3
      - uses: actions/setup-node@v3
      - uses: webfactory/ssh-agent@v0.7.0
          ssh-private-key: $

      - run: npm ci
      - run: npm test
      - run: npm run docs

      - uses: cpina/github-action-push-to-another-repository@v1.5.1
          SSH_DEPLOY_KEY: $
          destination-github-username: Mafalda-SFU
          source-directory: docs
          target-directory: docs/$
          user-name: Mafalda bot

Generate the documentation

To automatically generate the documentation, we have two aproaches: generate it as a git hook, or do it on the CI servers. I use to prefer the first option, specially for complex projects where people of different levels are working on the code (like Juniors & Seniors, or new employees), or for the projects where the documentation is going to be directly published on Github Pages (like open source projects) so the documentation is close to the code as reference, and also it’s possible to see how it has evolved during the time. But since it’s not possible to publish it as I’ve already said it before (if not, I would not be writing this post :-) ), it has had more weight my policy of not having generated code or artifacts stored as part of the source code of the git repository itself, so I decided to generate the documentation on the CI servers.

To generate the documentation, I’m using the jsdoc-to-markdown package. This imply to need to install the project dependencies on the CI servers, and this is where the problem arises: since I have not published any of the Mafalda SFU dependencies as a npm package, I need to use them as git dependencies, and being private ones, the Github Actions CI servers needs permissions to access to them. In normal conditions where only it’s accessed the repo itself, or when using private packages from the Github Packages Registry, it’s enough with the GITHUB_TOKEN secret or with a Personal Access Token, but since we’re using git dependencies, it’s not possible to use them to authenticate the git requests, only possible is with git credentials and/or an SSH key pair.

The first thing I’ve done is to create a new machine user account to authenticate and operate from Github Actions. This is for security, I could have used my own account, but then all operations would have been done in my name. This way, it’s possible to have a separate user with the lowest needed permissions (in this case just only read access to the private repositories, that’s the one set when adding an user as one of the organization members by default), and also it’s possible to revoke the access to the repositories if needed. After that, I’ve created a new SSH key pair, and added the public key to the Github machine user account I’ve just created before, so it can operate on the repositories

After that, what we need to do is to add the private key to the Github Actions, so it can be available when trying to install the git dependencies. This can be done with the ssh-agent action, that registers globally the provided private key. To do so, we need to set the private key as one of the repository secrets (it’s not possible to add it as an organization level secret on free plans), and then use it in the config of the ssh-agent action in the ssh-private-key parameter. Just with that, we can be able to install the npm git dependencies from Github Actions CI servers, and generate our documentation.

Publish the documentation

Once that we have the documentation generated, it’s time to copy it to the main repository. This is done with the github-action-push-to-another-repository action, that can push the contents of a directory to another repository different of the one where the action is running on. The config of the action is pretty straighforward, just setting the source directory from where to copy the files, the destination repository name, the Github username/organization that owns the destination repository, and the target directory where to copy them (this is important, by default it fully wipes the target repository). Just by config that parameters it would work, but commits would be mostly annonimous, so it’s better to also set the user name and user email that will be used to commit the changes.

The only tricky part of configuring github-action-push-to-another-repository is the access to the repository itself, since we need to provide another credentials with write access. The most safe way to do it is to create a new SSH deploy key that will be used to provide write access only on the destination repository, in this case the main documentation one. This is done by creating a new SSH key pair, and adding the public key to the destination repository as a deploy key with write access. Then, we need to add the private key as one of the repository secrets, and use it in the config of the action in the SSH_DEPLOY_KEY. After that, each time that the action is executed, it will push the generated documentation to the main repository, creating a new commit with the user email and name that we provided, and a commit message pointing to the original commit in the source repository where we generated the documentation from, having this way a two-ways cross-reference.

Written on December 25, 2022

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