Gcloud App Engine: connection to Google Cloud SQL

Nodejs application connects to database from localhost, but throws error after deployment:

From mysqljs:

Error: Cannot enqueue Query after fatal error. at Protocol._validateEnqueue

The http request returns status code 500

I am pretty sure that the issue is about authorization. App Engine is in the same project as SQL, however I've added app to the Authorize apps of SQL Instance:

gcloud sql instances patch <sql-instance> --authorized-gae-apps <app-name>

but this still did not work

via Maxim