BigQuery

You'd need to issue an auth key on Big Query/Google API portal:
https://cloud.google.com/bigquery/docs/authentication

Copy and paste the key right here:
https://app.getconduit.app/integrations/bigquery/connect/

The "Access Denied" issue

Permissions denied error while accessing or querying BigQuery shared dataset.

User does not have bigquery.jobs.create permission in project

Please read
https://cloud.google.com/knowledge/kb/permissions-denied-while-querying-bigquery-shared-dataset-000004323