Auth via Google's `auth` GitHub Action

[jennybc]

https://cloud.google.com/blog/products/identity-security/enabling-keyless-authentication-from-github-actions

Given that gargle already supports Application Default Credentials, I am optimistic it won't be too hard to make use of this.

[gvelasq]

Thank you for considering this functionality. I have been trying to build a GitHub Action that uses the YouTube Data API v3, and it would be great to be able to do it all without having to upload a secret. I haven't had luck finding a flow in httr, httr2, or gargle that can handle the access_token returned from the auth GitHub Action:

on: [push]

name: youtube-api-test

jobs:
  youtube-api-test:
    runs-on: macOS-latest
    permissions:
      contents: 'read'
      id-token: 'write'
    steps:
      - uses: actions/checkout@v3
        with:
          fetch-depth: 0
      - id: 'auth'
        name: 'Authenticate to Google Cloud'
        uses: 'google-github-actions/auth@v0'
        with:
          token_format: 'access_token'
          workload_identity_provider: 'projects/977381217576/locations/global/workloadIdentityPools/youtube-data-api/providers/youtube-data-api'
          service_account: '[email protected]'
      - uses: r-lib/actions/setup-r@v2
      - uses: r-lib/actions/setup-r-dependencies@v2
        with:
          cache-version: 2
      - name: 'Explore access_token names'
        run: |
          Rscript -e 'access_token <- jsonlite::fromJSON(Sys.getenv("GOOGLE_APPLICATION_CREDENTIALS"))' \
                  -e 'names(access_token)'

This returns the following names:

[1] "type"                              "audience"                         
[3] "subject_token_type"                "token_url"                        
[5] "service_account_impersonation_url" "credential_source"

Since some R API wrapper package functions (e.g., tuber::list_channel_videos()) expect a httr::oauth2.0_token(), would this auth flow permit the resulting WifToken or other returned files to be compatible with different R API wrapper packages depending on whether they were implemented in httr, httr2, or gargle?