This is a GitHub Action that can be used to get scoped limited access, expiring credentials for use inside GitHub Actions Workflows.

Why would you want to do this? Well the GITHUB_TOKEN whilst having an expiry, has some protections around creating events that prevent downstream GitHub Actions workflow from triggering. This prevents recursive loops from workflows, but there are a number of valid types of workflows that may require or desire triggering downstream GitHub Actions Workflows.

The existing way to work around this today is to use a Personal Access Token, but these tokens are tied to a user and generally are over priviledged for the tasks at hand, increasing the risk if they get exposed and are not time limited like the GITHUB_TOKEN.

This is where a GitHub Application access token can really help out. The benefits of GitHub Applications is that you can restrict/scope the access of the token considerably more than what can be achieved using a Personal Access Token. The access token from the GitHub Application is also time limited, expiring after an hour from being issued, providing some more protection against any leaking of credentials from a Workflow.

To use this action you first need a GitHub Application created so that you can request temporary credentials on behalf of the application inside your workflows.

Requirements:

• A new or existing GitHub Application with the access scopes required
• A private key for the GitHub Application
• The GitHub Application installed on the repository that the GitHub Actions Workflow will execute from

You will need to have a GitHub Application that is scoped with the necessary permissions for the token that you want to retrieve at runtime.

To create a GitHub Application you can follow the steps available at https://docs.github.com/en/developers/apps/creating-a-github-app

The important configuration details for the application are:

• GitHub App name a human readable application name that is unique within GitHub.com
• Description some details about your application and what you intend to use it for
• Homepage URL needs to be set to something as long as it is a URL
• Expire user authorization tokens should be checked so as to expire any tokens that are issued
• Webhook Active checkbox should be unchecked
• Repository permissions, Organization permissions and/or User permissions should be set to allow the access required for the token that will be issued
• Where can this GitHub App be installed? should be scoped to your desired audience (the current account, or any account)

Once the application has been created you will be taken to the General settings page for the new application. The GitHub Application will be issued an App ID which you can see in the About section, take note of this for later use in the Actions workflow.

On the General settings page for the application, at the bottom there is a Private keys section that you can use to generate a private key that can be utilized to authenticate as the application. Generate a new private key and store the information for later use.

Note: the private keys can and should be rotated periodically to limit the risks of them being exposed in use.

Once you have the GitHub Application defined, you will need to install the application on the target repository or repositories that you want it to have access to. These will be any repositories that you want to gather information from or want the application to modify as per the scopes that were defined when the application was installed.

Note: The GitHub Application will need to be installed on the repository that you are executing the GitHub Actions workflow from, as the implementation requires this before it will generate access tokens for you.

To use the action in a worklow, it is recommended that you store the GitHub Application Private key in GitHub Secrets. This can be done at a repository or organization level (provided that the actions workflow has access to the secret).

When storing the Private key, you can store the raw PEM encoded certificate contents that the GitHub Application generates for you or Base64 encode it in the secret.

• application_id: The GitHub Application ID that you wil be getting the access token for
• application_private_key: A private key generated for the GitHub Application so that you can authenticate (PEM format or base64 encoded)

jobs:
  get-temp-token:
    runs-on: ubuntu-latest

    steps:
      - name: Get Token
        id: get_workflow_token
        uses: peter-murray/workflow-application-token-action@v1
        with:
          application_id: ${{ secrets.APPLICATION_ID }}
          application_private_key: ${{ secrets.APPLICATION_PRIVATE_KEY }}
        
      - name: Use Application Token to create a release
        uses: actions/create-release@v1
        env:
          GITHUB_TOKEN: ${{ steps.get_workflow_token.outputs.token }}
        with:
          ....

https://docs.github.com/en/developers/apps/authenticating-with-github-apps#authenticating-as-an-installation