Expired authentication credentials are reported as HTTP 503 (Service Unavailable) errors

Reproduce the failure from stormware/google/secrets.py at line 71 using expired credentials, then trace the generated Secret Manager client through google/api_core/gapic_v1/method.py and google/api_core/retry/retry_unary.py. Done means expired-credential failures surface immediately as an authentication error rather than being retried as HTTP 503 until the 60-second timeout.

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Summary of the issue

Context
Whenever we try to use the SDK clients with expired authentication credentials our programs halt for 60 seconds. This is because such requests get a 503 HTTP response back (which is not the correct response), so the library keeps retrying until the default timeout (which is 60 seconds).

Expected Behavior:
We expect SDK clients to fail immediately when credentials are expired.

Actual Behavior:
SDK clients do not fail immediately when credentials are expired.

API client name and version

google-cloud-secret-manager==2.30.0

Reproduction steps: code

See https://github.com/logikal-io/stormware/blob/main/stormware/google/secrets.py#L71.

Reproduction steps: supporting files

No response

Reproduction steps: actual results

The errors seen are as follows:

  File ".../lib/python3.12/site-packages/stormware/google/secrets.py", line 71, in __getitem__
    response = self.client.access_secret_version(name=name)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/google/cloud/secretmanager_v1/services/secret_manager_service/client.py", line 1875, in access_secret_version
    response = rpc(
               ^^^^
  File ".../lib/python3.12/site-packages/google/api_core/gapic_v1/method.py", line 373, in __call__
    result = wrapped_func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/google/api_core/retry/retry_unary.py", line 295, in retry_wrapped_func
    return retry_target(
           ^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/google/api_core/retry/retry_unary.py", line 157, in retry_target
    next_sleep = _retry_error_helper(
                 ^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/google/api_core/retry/retry_base.py", line 230, in _retry_error_helper
    raise final_exc from source_exc
google.api_core.exceptions.RetryError: Timeout of 60.0s exceeded, last exception: 503 Getting metadata from plugin failed with error: Reauthentication is needed. Please run `gcloud auth application-default login` to reauthenticate.

Reproduction steps: expected results

We'd expect these calls to fail immediately.

OS & version + platform

No response

Python environment

No response

Python dependencies

No response

Additional context

No response