Google Drive OAuth authorization fails with Error 403: access_denied (unverified app / testing mode) #938

Describe the bug
When attempting to link a Google Drive account on dillinger.io, Google OAuth blocks the connection request, displaying an unverified app warning and an Error 403: access_denied.

To Reproduce
Steps to reproduce the behavior:

1. Navigate to dillinger.io.
2. Click on the Google Drive export/import connection option.
3. Select a Google account to sign in.
4. See the Google OAuth error page stating: "Access blocked: dillinger.io has not completed the Google verification process."

Expected behavior
The Google OAuth consent screen should allow standard users to grant permission to access Google Drive.

Error Message:
Access blocked: dillinger.io has not completed the Google verification process.
The app is currently being tested, and can only be accessed by developer-approved testers. If you think you should have access, contact the developer.
Error 403: access_denied

OAuth Request Parameters:
Request details:
access_type=offline
scope=openid https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/drive
response_type=code
redirect_uri=https://dillinger.io/api/google-drive/callback
prompt=consent
flowName=GeneralOAuthFlow
client_id=240056957115-3d8ticoo7c097h03afadj90t9cmk2435.apps.googleusercontent.com

Possible Cause
The GCP OAuth Client / App publishing status appears to be set to "Testing" rather than "In Production", or the sensitive scope (https://www.googleapis.com/auth/drive) requires re-verification by Google.