only enable feature if auth library has support

Author: andrewsg

google/cloud/client/__init__.py

@@ -25,12 +25,18 @@
 import google.api_core.exceptions
 import google.auth
 from google.auth import environment_vars
-import google.auth.api_key
 import google.auth.credentials
 import google.auth.transport.requests
 from google.cloud._helpers import _determine_default_project
 from google.oauth2 import service_account
 
+try:
+    import google.auth.api_key
+
+    HAS_GOOGLE_AUTH_API_KEY = True
+except:
+    HAS_GOOGLE_AUTH_API_KEY = False
+
 
 _GOOGLE_AUTH_CREDENTIALS_HELP = (
     "This library only supports credentials from google-auth-library-python. "
@@ -162,7 +168,11 @@ def __init__(self, credentials=None, _http=None, client_options=None):
                 "'credentials' and 'client_options.credentials_file' are mutually exclusive."
             )
 
-        if client_options.api_key and (credentials or client_options.credentials_file):
+        if (
+            HAS_GOOGLE_AUTH_API_KEY
+            and client_options.api_key
+            and (credentials or client_options.credentials_file)
+        ):
             raise google.api_core.exceptions.DuplicateCredentialArgs(
                 "'client_options.api_key' is mutually exclusive with 'credentials' and 'client_options.credentials_file'."
             )
@@ -180,7 +190,7 @@ def __init__(self, credentials=None, _http=None, client_options=None):
                 credentials, _ = google.auth.load_credentials_from_file(
                     client_options.credentials_file, scopes=scopes
                 )
-            elif client_options.api_key is not None:
+            elif HAS_GOOGLE_AUTH_API_KEY and client_options.api_key is not None:
                 credentials = google.auth.api_key.Credentials(client_options.api_key)
             else:
                 credentials, _ = google.auth.default(scopes=scopes)

tests/unit/test_client.py

@@ -17,6 +17,8 @@
 import unittest
 from unittest import mock
 
+from google.cloud.client import HAS_GOOGLE_AUTH_API_KEY
+
 
 def _make_credentials():
     import google.auth.credentials
@@ -75,6 +77,9 @@ def test_ctor_explicit(self):
         self.assertIs(client_obj._credentials, credentials)
         self.assertIs(client_obj._http_internal, http)
 
+    @unittest.skipIf(
+        not HAS_GOOGLE_AUTH_API_KEY, "Auth library version does not support API keys"
+    )
     def test_ctor_client_options_w_api_key(self):
         from google.auth.api_key import Credentials
 
@@ -93,6 +98,9 @@ def test_ctor_client_options_w_conflicting_creds(self):
         with self.assertRaises(DuplicateCredentialArgs):
             self._make_one(credentials=credentials, client_options=client_options)
 
+    @unittest.skipIf(
+        not HAS_GOOGLE_AUTH_API_KEY, "Auth library version does not support API keys"
+    )
     def test_ctor_client_options_w_api_key_and_conflicting_creds(self):
         from google.api_core.exceptions import DuplicateCredentialArgs