Add back support for sigv4 overrides

This allows you to change the signature version used when
signing requests for a particular service.

This isn't strictly needed to communicate with various endpoints,
any region specific signature versions are captured in _endpoints.json.
However, with S3 we sometimes need to switch to sigv4 even if it
otherwise wouldn't be required.

botocore/handlers.py

@@ -270,7 +270,8 @@ def signature_overrides(service_data, service_name, session, **kwargs):
         logger.debug("Switching signature version for service %s "
                      "to version %s based on config file override.",
                      service_name, signature_version_override)
-        service_data['signature_version'] = signature_version_override
+        service_metadata = service_data['metadata']
+        service_metadata['signatureVersion'] = signature_version_override
 
 
 def add_expect_header(model, params, **kwargs):

tests/integration/test_s3.py

@@ -560,5 +560,26 @@ def test_can_get_bucket_location(self):
         self.assertEqual(response[1]['LocationConstraint'], 'eu-central-1')
 
 
+class TestCanSwitchToSigV4(unittest.TestCase):
+    def setUp(self):
+        self.session = botocore.session.get_session()
+
+    def test_verify_can_switch_sigv4(self):
+        self.session.set_config_variable('s3', {'signature_version': 's3v4'})
+        # We need to verify this option for service/operation objects so we're
+        # not using client objects now (though we should add a test for client
+        # objects eventually).
+        service = self.session.get_service('s3')
+        endpoint = service.get_endpoint('us-east-1')
+        # The set_config_variable should ensure that we use sigv4 for s3.
+        self.assertIsInstance(endpoint.auth, botocore.auth.S3SigV4Auth)
+
+        # And just to be sure, we'll go ahead and make a basic S3
+        # call and verify it works with sigv4.
+        operation = service.get_operation('ListBuckets')
+        http, response = operation.call(endpoint)
+        self.assertEqual(http.status_code, 200)
+
+
 if __name__ == '__main__':
     unittest.main()

tests/unit/test_handlers.py

@@ -52,19 +52,23 @@ def test_switch_to_sigv4(self):
         mock_session.get_scoped_config.return_value = {
             's3': {'signature_version': 's3v4'}
         }
-        kwargs = {'service_data': {'signature_version': 's3'},
+        kwargs = {'service_data': {'metadata': {'signatureVersion': 's3'}},
                   'service_name': 's3', 'session': mock_session}
         self.session.emit(event, **kwargs)
-        self.assertEqual(kwargs['service_data']['signature_version'], 's3v4')
+        self.assertEqual(
+            kwargs['service_data']['metadata']['signatureVersion'],
+            's3v4')
 
     def test_noswitch_to_sigv4(self):
         event = self.session.create_event('service-data-loaded', 's3')
         mock_session = mock.Mock()
         mock_session.get_scoped_config.return_value = {}
-        kwargs = {'service_data': {'signature_version': 's3'},
+        kwargs = {'service_data': {'metadata': {'signatureVersion': 's3'}},
                   'service_name': 's3', 'session': mock_session}
         self.session.emit(event, **kwargs)
-        self.assertEqual(kwargs['service_data']['signature_version'], 's3')
+        self.assertEqual(
+            kwargs['service_data']['metadata']['signatureVersion'],
+            's3')
 
     def test_quote_source_header(self):
         for op in ('UploadPartCopy', 'CopyObject'):