Allow nbgitpuller to pull from private GitHub repos#

nbgitpuller is very popularly used to pull repos from public GitHub repositories. We can also allow users to pull from private GitHub repositories, with git-credential-helpers.

When supporting a cluster of hubs for use by the same community (such as a large university), we can use the same GitHub app for all of the hubs (unless explicitly requested to not). This simplifies instructors workflow.

Configure the image#

The image used in the JupyterHub must have the git-credential-helpers package installed from PyPI. Unfortunately this is currently not installed in any common upstream images, so this will only work with custom images.

Setup GitHub app#

git-credentials-helper uses a GitHub App to pull private repos. So you first need to create a GitHub app for each hub that wants to pull private repos as static content.

Create a GitHub app in the 2i2c org.
Give it a descriptive name (such as ‘ private repo access’) and description, as users will see this when authorizing access to their private repos.
Disable webhooks (uncheck the ‘Active’ checkbox under ‘Webhooks’). All other textboxes can be left empty.
Under ‘Repository permissions’, select ‘Read’ for ‘Contents’.
Under ‘Where can this GitHub App be installed?’, select ‘Any account’. This will enable users to push to their own user repositories or other organization repositories, rather than just the 2i2c repos.
Create the application with the ‘Create GitHub app’ button.
Copy the numeric ‘App id’ from the app info page you should be redirected to.
Create a new private key for authentication use with the Generate a private key button. This should download a private key file, that you should delete after putting it in the appropriate config (in the next step)

Helm values configuration#

Now, we configure our user servers to authenticate themselves with GitHub using the app we just created.

Tell git to use our GitHub app for authenticating when cloning from GitHub.
```
jupyterhub:
  singleuser:
    extraFiles:
      gitconfig:
        mountPath: <path-to-git-config>
        stringData: |
          [credential "https://github.com"]
          helper = !git-credential-github-app --app-key-file /etc/github/github-app-private-key.pem --app-id <app-id>
          useHttpPath = true
```
Unfortunately, the <path-to-git-config> depends on how git is installed inside the image.

a. The most common situation is git is installed from apt or the system package manager, and not conda. In this case, mountPath is /etc/gitconfig.

b. If git is installed from conda, it will not read /etc/gitconfig (see bug, but ${CONDA_PREFIX}/etc/gitconfig. So, if the image installs git from conda-forge, you have to start the image, look for the value of the ${CONDA_PREFIX} environment variable, and construct mountPath to be ${CONDA_PREFIX}/etc/gitconfig

Use the app-id of the GitHub app you just created. This goes in the hub’s values.yaml file. If used for a daskhub, next the whole thing under a basehub key.
Create a sops-encrypted file (usually in the form of enc-<hub-name>.secret.values.yaml) to hold the secret values required to authenticate the GitHub app.
```
jupyterhub:
  singleuser:
    extraFiles:
      github-app-private-key.pem:
        mountPath: /etc/github/github-app-private-key.pem
        stringData: |
          <contents-of-the-private-key-file>
         
```
Make sure this file is also listed under helm_chart_values_files for the hub in the cluster’s cluster.yaml so it is read during deployment.
Once set up, do a deploy to test!

Grant access to the private repo#

Finally, someone with admin rights on the private repo to be pulled needs to grant the github app we just setup access to the private repo. This is the only part that hub admins rather than 2i2c engineers need to do.

Go to the ‘Public page’ of the GitHub app created. This usually is of the form https://github.com/apps/<name-of-app>. You can find this in the information page of the app after you create it, under ‘Public link’
Install the app in the organization the private repo is in, and grant it access only to the repo that needs to be pulled.

Create the nbgitpuller link#

An nbgitpuller link can be created now for this private repo with the usual mechanisms:

The nbgitpuller.link generator
The Firefox or Chrome extensions.

Allow nbgitpuller to pull from private GitHub repos

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