Fixing server failure on missing request credential

This change fixes a bug in the KMIP server engine where a missing
request credential would cause the session to prematurely
terminate. Credential handling may require session termination
for missing credentials, but that decision should be made by
credential processing not request processing.

Fixes #193

kmip/services/server/engine.py

@@ -249,7 +249,10 @@ class KmipEngine(object):
             )
 
         # Process the authentication credentials
-        auth_credentials = header.authentication.credential
+        if header.authentication:
+            auth_credentials = header.authentication.credential
+        else:
+            auth_credentials = None
         self._verify_credential(auth_credentials, credential)
 
         # Process the batch error continuation option

kmip/tests/unit/services/server/test_engine.py

@@ -391,6 +391,41 @@ class TestKmipEngine(testtools.TestCase):
             *args
         )
 
+    def test_process_request_missing_credential(self):
+        """
+        Test that the engine does not immediately error out when retrieving
+        a non-existent credential from the request.
+        """
+        e = engine.KmipEngine()
+        e._logger = mock.MagicMock()
+
+        protocol = contents.ProtocolVersion.create(1, 1)
+        header = messages.RequestHeader(
+            protocol_version=protocol,
+            authentication=None,
+            batch_error_cont_option=contents.BatchErrorContinuationOption(
+                enums.BatchErrorContinuationOption.STOP
+            ),
+            batch_order_option=contents.BatchOrderOption(True),
+            time_stamp=contents.TimeStamp(int(time.time())),
+            batch_count=contents.BatchCount(1)
+        )
+        payload = discover_versions.DiscoverVersionsRequestPayload()
+        batch = list([
+            messages.RequestBatchItem(
+                operation=contents.Operation(
+                    enums.Operation.DISCOVER_VERSIONS
+                ),
+                request_payload=payload
+            )
+        ])
+        request = messages.RequestMessage(
+            request_header=header,
+            batch_items=batch
+        )
+
+        e.process_request(request)
+
     def test_build_error_response(self):
         """
         Test that a bare bones response containing a single error result can