Why doesn't gcsfs allow projects different from the default project in google_default?

With account which has $ gcloud config get-value project # => project-a,

fs = gcsfs.GCSFileSystem(project='project-b')

raise validation error:

ValueError: User-provided project 'project-b' does not match the google default project 'project-a'. Either

  1. Accept the google-default project by not passing a `project` to GCSFileSystem
  2. Configure the default project to match the user-provided project (gcloud config set project)
  3. Use an authorization method other than 'google_default' by providing 'token=...'

However, I do want to use another project. Why gcsfs doesn't allow this?

My google_default account has correct permission to access project-b so it's no problem to access from the account. (I believe the account's default project doesn't matter.)

For option2, I use multiple fs objects for multiple projects with single google_default account, so I can't switch default project (gcloud config set project) to match.

For option3, I would like to use the Application Default Credential mechanism to make it work conveniently both on cloud and local.

Start by reproducing the GCSFileSystem(project='project-b') case with google_default while gcloud config uses project-a. Trace the google_default validation that rejects the mismatch and verify how Application Default Credentials are selected. Done means separate filesystem objects can target different projects without changing the gcloud default, with regression coverage for this case.