[kmelnikov]

Summary

Generated REST transports (<Service>RestTransport) accept credentials_file, scopes, quota_project_id, and client_cert_source_for_mtls in __init__, but previously dropped several of those arguments instead of forwarding them to the base transport or applying them consistently with GrpcTransport:

1. Forward credentials_file, scopes, and quota_project_id in REST transports: <Service>RestTransport.__init__ and _Base<Service>RestTransport.__init__ now pass credentials_file, scopes, and quota_project_id through super().__init__(...) to <Service>Transport.__init__ (resolving the TODO(yon-mg): resolve other ctor params i.e. scopes, quota, etc. in rest.py.j2), so Application Default Credentials (google.auth.default) and file-loaded credentials (google.auth.load_credentials_from_file) receive quota_project_id and scopes under transport="rest" just like transport="grpc".
2. Apply scopes and quota_project_id to explicit credentials in base.py.j2: When explicit credentials are passed to <Service>Transport, ga_credentials.with_scopes_if_required(credentials, scopes=scopes, default_scopes=self.AUTH_SCOPES) and credentials.with_quota_project(quota_project_id) (when isinstance(credentials, ga_credentials.CredentialsWithQuotaProject)) are now applied in the base transport, matching google.api_core.grpc_helpers._create_composite_credentials.
3. Forward client_cert_source_for_mtls to OperationsRestTransport: <Service>RestTransport now stores self._client_cert_source_for_mtls = client_cert_source_for_mtls and passes it to operations_v1.OperationsRestTransport(...) when constructing operations_client.
4. Tests & Goldens:
   • Added unit tests in packages/gapic-generator/tests/unit/generator/test_rest_transport_auth.py.
   • Updated test_%service.py.j2 to include <Service>RestTransport in test_<service>_transport_auth_adc and added test_<service>_base_transport_with_credentials.
   • Updated the integration golden files in packages/gapic-generator/tests/integration/goldens/.

[gemini-code-assist]

Code Review

This pull request updates the GAPIC generator templates and golden files to correctly forward and apply scopes, quota project IDs, and credentials files in REST transports. It also introduces a new test suite to verify REST transport authentication. The code review identified a critical runtime issue in the base transport template where CredentialsWithQuotaProject is incorrectly accessed from google.api_core.credentials instead of google.auth.credentials, which would lead to an AttributeError.