Get project id from google.auth.default() in empty GcpCredentials block if quota project is None

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fix `list_folders` and `list_blobs` now logging bucket name and bucket path - [#184](https://github.com/PrefectHQ/prefect-gcp/pull/214)
+- Fix empty `GcpCredentials` not inferring the GCP project upon initialization when running on Compute Engine, Cloud Run, and App Engine - [#219](https://github.com/PrefectHQ/prefect-gcp/pull/219)
 
 ### Security
 

prefect_gcp/credentials.py

@@ -164,8 +164,12 @@ def block_initialization(self):
         if self.project is None:
             if self.service_account_info or self.service_account_file:
                 credentials_project = credentials.project_id
-            else:  # google.auth.default using gcloud auth application-default login
+            # google.auth.default using gcloud auth application-default login
+            elif credentials.quota_project_id:
                 credentials_project = credentials.quota_project_id
+            # compute-assigned service account via GCP metadata server
+            else:
+                _, credentials_project = google.auth.default()
             self.project = credentials_project
 
         if hasattr(credentials, "service_account_email"):

tests/conftest.py

@@ -42,6 +42,20 @@ def google_auth(monkeypatch):
     return google_auth_mock
 
 
+@pytest.fixture
+def google_auth_no_quota_project(monkeypatch):
+    google_auth_mock = MagicMock()
+    default_credentials_mock = MagicMock(
+        client_id="my_client_id", quota_project_id=None
+    )
+    google_auth_mock.default.side_effect = lambda *args, **kwargs: (
+        default_credentials_mock,
+        "my_project",
+    )
+    monkeypatch.setattr("google.auth", google_auth_mock)
+    return google_auth_mock
+
+
 @pytest.fixture
 def oauth2_credentials(monkeypatch):
     CredentialsMock = MagicMock()

tests/test_credentials.py

@@ -108,6 +108,13 @@ def test_block_initialization_gcloud_cli(google_auth, oauth2_credentials):
     assert gcp_credentials.project == "my_project"
 
 
+def test_block_initialization_metadata_server(
+    google_auth_no_quota_project, oauth2_credentials
+):
+    gcp_credentials = GcpCredentials()
+    assert gcp_credentials.project == "my_project"
+
+
 @pytest.mark.parametrize("override_project", [None, "override_project"])
 def test_get_cloud_storage_client(
     override_project, service_account_info, oauth2_credentials, storage_client