setting up airflow with bigquery operator

If you need to do this programmatically, I use this as an entrypoint in our stack to create the connection if it doesn't already exist:

from airflow.models import Connection
from airflow.settings import Session

session = Session()
gcp_conn = Connection(
    conn_id='bigquery',
    conn_type='google_cloud_platform',
    extra='{"extra__google_cloud_platform__project":"<YOUR PROJECT HERE>"}')
if not session.query(Connection).filter(
        Connection.conn_id == gcp_conn.conn_id).first():
    session.add(gcp_conn)
    session.commit()

Took me a while to finally find it as it's not documented very clearly. In the airflow UI, go to Admin -> Connection. That connection id is what is being referenced by the parameters bigquery_connection_id. You must add in the "extras" field a json object that defines a k,v pair of "project" : ""

You must also add keys for "service_account" and "key_path" if you have not explicitly authorized an account on the box you're running Airflow. (gcloud auth)