allow zuul to have multiple values for each named header

fixes gh-260

spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/zuul/filters/ProxyRequestHelper.java

@@ -76,13 +76,16 @@ public class ProxyRequestHelper {
 			HttpServletRequest request) {
 		RequestContext context = RequestContext.getCurrentContext();
 		MultiValueMap<String, String> headers = new LinkedMultiValueMap<>();
-		Enumeration<?> headerNames = request.getHeaderNames();
+		Enumeration<String> headerNames = request.getHeaderNames();
 		if (headerNames != null) {
 			while (headerNames.hasMoreElements()) {
-				String name = (String) headerNames.nextElement();
-				String value = request.getHeader(name);
-				if (isIncludedHeader(name)) {
-					headers.set(name, value);
+				String name = headerNames.nextElement();
+                if (isIncludedHeader(name)) {
+                    Enumeration<String> values = request.getHeaders(name);
+                    while (values.hasMoreElements()) {
+                        String value = values.nextElement();
+                        headers.add(name, value);
+                    }
 				}
 			}
 		}

spring-cloud-netflix-core/src/test/java/org/springframework/cloud/netflix/zuul/filters/ProxyRequestHelperTests.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2013-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.netflix.zuul.filters;
+
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.springframework.boot.actuate.trace.TraceRepository;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.util.MultiValueMap;
+
+import static org.junit.Assert.*;
+import static org.hamcrest.Matchers.*;
+import static org.mockito.MockitoAnnotations.initMocks;
+
+/**
+ * @author Spencer Gibb
+ */
+public class ProxyRequestHelperTests {
+
+    @Mock
+    private TraceRepository traceRepository;
+
+    @Before
+    public void init() {
+        initMocks(this);
+    }
+
+    @Test
+    public void buildZuulRequestHeadersWork() {
+        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/");
+        request.addHeader("singleName", "singleValue");
+        request.addHeader("multiName", "multiValue1");
+        request.addHeader("multiName", "multiValue2");
+
+        ProxyRequestHelper helper = new ProxyRequestHelper();
+        helper.setTraces(traceRepository);
+
+        MultiValueMap<String, String> headers = helper.buildZuulRequestHeaders(request);
+        List<String> singleName = headers.get("singleName");
+        assertThat(singleName, is(notNullValue()));
+        assertThat(singleName.size(), is(1));
+
+        List<String> multiName = headers.get("multiName");
+        assertThat(multiName, is(notNullValue()));
+        assertThat(multiName.size(), is(2));
+
+        List<String> missingName = headers.get("missingName");
+        assertThat(missingName, is(nullValue()));
+
+    }
+}