How can you validate that data written to BigQuery was done using the App Engine Default Service Account?

Using Cloud Logging to filter on BigQuery Insert Jobs is indeed the most effective way to validate that data written to BigQuery was done using the App Engine Default Service Account. Cloud Logging captures detailed logs of operations and activities across Google Cloud services, including BigQuery. When you filter the logs specifically for Insert Jobs in BigQuery, you can view entries that will show which service account was responsible for the data insert operation. This detailed logging allows you to confirm the identity of the service account that performed the actions, making it a reliable method for validation.

Additionally, while checking the logs on Cloud Storage could provide some context about files or data changes, it does not directly correlate to the BigQuery insert operations and is therefore less relevant for this particular question. Requesting a report from BigQuery on data access could provide information about who accessed the data or executed queries, but it wouldn’t confirm the identity of the account that wrote the data. Lastly, examining the IAM permissions of the project would tell you about what roles and permissions are assigned, but it would not give specific insights into actions that were taken or which accounts performed those actions, limiting its effectiveness in this context.