Use Google Auth's load_credentials_from_* Methods

These methods handle services accounts as well any any other credential
method. Got someone using DBT with AWS-based Auth (see #86)? This will
work with AWS Auth.

Typical service account auth with a key file and oauth2 jwt assertion grant
stuff still works and is covered here: https://github.com/googleapis/google-auth-library-python/blob/v2.14.1/google/auth/_default.py#L408

I did add `google-auth>=2.20.0` which is the first version that has
`load_credentials_from_dict`. Previously this lower bound was v2.14.1
(from `google-api-core>=2.11`).

Basically this will just let folks auth bigquery however they would auth
any gcloud resources without any extra effort. And the previous versions
config still works exactly the same.

Author: chrisguitarguy

dbt/adapters/bigquery/connections.py

@@ -18,12 +18,12 @@
 import google.cloud.bigquery as bigquery
 import google.cloud.exceptions
 from google.api_core import retry, client_info
-from google.auth import impersonated_credentials
-from google.oauth2 import (
-    credentials as GoogleCredentials,
-    service_account as GoogleServiceAccountCredentials,
+from google.auth import (
+    impersonated_credentials,
+    load_credentials_from_file,
+    load_credentials_from_dict,
 )
-
+from google.oauth2 import credentials as GoogleCredentials,
 from dbt.adapters.bigquery import gcloud
 from dbt.clients import agate_helper
 from dbt.config.profile import INVALID_PROFILE_MESSAGE
@@ -332,19 +332,20 @@ def format_rows_number(self, rows_number):
     @classmethod
     def get_google_credentials(cls, profile_credentials) -> GoogleCredentials:
         method = profile_credentials.method
-        creds = GoogleServiceAccountCredentials.Credentials
 
         if method == BigQueryConnectionMethod.OAUTH:
             credentials, _ = get_bigquery_defaults(scopes=profile_credentials.scopes)
             return credentials
 
         elif method == BigQueryConnectionMethod.SERVICE_ACCOUNT:
             keyfile = profile_credentials.keyfile
-            return creds.from_service_account_file(keyfile, scopes=profile_credentials.scopes)
+            credentials, _ = load_credentials_from_file(keyfile, scopes=profile_credentials.scopes)
+            return credentials
 
         elif method == BigQueryConnectionMethod.SERVICE_ACCOUNT_JSON:
             details = profile_credentials.keyfile_json
-            return creds.from_service_account_info(details, scopes=profile_credentials.scopes)
+            credentials, _ = load_credentials_from_dict(details, scopes=profile_credentials.scopes)
+            return credentials
 
         elif method == BigQueryConnectionMethod.OAUTH_SECRETS:
             return GoogleCredentials.Credentials(

setup.py

@@ -81,6 +81,7 @@ def _dbt_core_version(plugin_version: str) -> str:
         # ----
         # Expect compatibility with all new versions of these packages, so lower bounds only.
         "google-api-core>=2.11.0",
+        "google-auth>=2.20.0",
     ],
     zip_safe=False,
     classifiers=[