Invalid Argument errors when using Vertex with `google-github-actions/auth`

[mattmoor]

I am using Vertex to access the Claude models via this SDK:

anthropic.NewClient(
	vertex.WithGoogleAuth(ctx, region, projectID),
),

I am attempting to federate from github actions to invoke some Go tests with:

      - uses: 'google-github-actions/auth@b7593ed2efd1c1617e1b0254da33b86225adb2a5' # v2.1.12
        with:
          workload_identity_provider: ...
          service_account: ...
          # I have tried with and without these:
          export_environment_variables: true
          create_credentials_file: true

I have enabled the models I am trying in the vertex "model garden", but all of the Claude models consistently result in the following error:

Post "https://us-east5-aiplatform.googleapis.com/v1/projects/.../locations/us-east5/publishers/anthropic/models/claude-sonnet-4@20250514:rawPredict": oauth2/google: status code 400: {  "error": {    "code": 400,    "message": "Request contains an invalid argument.",    "status": "INVALID_ARGUMENT"  }}

This works locally for me, so I suspect that this is something nuanced and specific to the github actions federated auth path, but I haven't been able to find a configuration that works (at least yet).