[Adapter Auth] BigQuery Workload Identity Federation (WIF) / External OAuth

Overview

Add support for GCP Workload Identity Federation (WIF) in the dbt-fusion BigQuery adapter.

WIF allows BigQuery authentication to be delegated to an external OIDC provider, enabling keyless auth flows commonly used in CI/CD environments and multi-cloud setups. This is a significant auth method for large BigQuery customers and is blocking Fusion adoption for some of them.

What needs to be implemented

The BigQuery adapter should support the external_oauth / WIF credential path. The reference implementation in dbt-adapters can be found here:

https://github.com/dbt-labs/dbt-adapters/blob/1f3f529dc713f493a74514feb3ab239ed7fc7cf6/dbt-bigquery/src/dbt/adapters/bigquery/credentials.py#L254

Reference

• Upstream tracking issue: dbt-labs/fs#1958
• Auth methods guide (internal): https://www.notion.so/dbtlabs/Adapters-Auth-Methods-Front-End-Team-Guide-1d0bb38ebda780f8a597e80466f8f129?pvs=4#1d0bb38ebda780cc8c1bd35a11696995