Override None timeout with a default one

Until all dependent libraries expose configurable timeouts, we do
not want to accept an accidentally passed None timeout.

Assumption: there are no good real-world use cases where a None
timeout would be desirable, as that can make a request to hang
indefinitely.

google/auth/transport/requests.py

@@ -289,6 +289,13 @@ def request(
         # thread-safety.
         _credential_refresh_attempt = kwargs.pop("_credential_refresh_attempt", 0)
 
+        # Until all libraries expose explicit timeouts, a rouge None timeout
+        # might sneak in - for example, a default timeout value in one of the
+        # internal classes. Since it's desired to have at least some timeout,
+        # we override any `None` values for now.
+        if timeout is None:
+            timeout = _DEFAULT_TIMEOUT
+
         # Make a copy of the headers. They will be modified by the credentials
         # and we want to pass the original headers if we recurse.
         request_headers = headers.copy() if headers is not None else {}

tests/transport/test_requests.py

@@ -192,6 +192,21 @@ def test_request_default_timeout(self):
         expected_timeout = google.auth.transport.requests._DEFAULT_TIMEOUT
         assert patched_request.call_args.kwargs.get("timeout") == expected_timeout
 
+    def test_request_overriding_none_timeouts(self):
+        credentials = mock.Mock(wraps=CredentialsStub())
+        response = make_response()
+        adapter = AdapterStub([response])
+
+        authed_session = google.auth.transport.requests.AuthorizedSession(credentials)
+        authed_session.mount(self.TEST_URL, adapter)
+
+        patcher = mock.patch("google.auth.transport.requests.requests.Session.request")
+        with patcher as patched_request:
+            authed_session.request("GET", self.TEST_URL, timeout=None)
+
+        expected_timeout = google.auth.transport.requests._DEFAULT_TIMEOUT
+        assert patched_request.call_args.kwargs.get("timeout") == expected_timeout
+
     def test_request_no_refresh(self):
         credentials = mock.Mock(wraps=CredentialsStub())
         response = make_response()