Change to fix issue not setting content type header

src/Ocelot/Request/Mapper/RequestMapper.cs

@@ -5,6 +5,7 @@
     using System.IO;
     using System.Linq;
     using System.Net.Http;
+    using System.Net.Http.Headers;
     using System.Threading.Tasks;
 
     using Microsoft.AspNetCore.Http;
@@ -44,7 +45,11 @@
                 return null;
             }
 
-            return new ByteArrayContent(await ToByteArray(request.Body));
+            var content = new ByteArrayContent(await ToByteArray(request.Body));
+
+            content.Headers.TryAddWithoutValidation("Content-Type", new[] {request.ContentType});
+
+            return content;
         }
 
         private HttpMethod MapMethod(HttpRequest request)

test/Ocelot.UnitTests/Request/Mapper/RequestMapperTests.cs

@@ -117,6 +117,35 @@
                 .BDDfy();
         }
 
+        [Fact]
+        public void Should_map_content_type_header()
+        {
+            this.Given(_ => GivenTheInputRequestHasContent("This is my content"))
+                .And(_ => GivenTheContentTypeIs("application/json"))
+                .And(_ => GivenTheInputRequestHasMethod("GET"))
+                .And(_ => GivenTheInputRequestHasAValidUri())
+                .When(_ => WhenMapped())
+                .Then(_ => ThenNoErrorIsReturned())
+                .And(_ => ThenTheMappedRequestHasContentTypeHeader("application/json"))
+                .And(_ => ThenTheMappedRequestHasContentSize("This is my content".Length))
+                .BDDfy();
+        }
+
+        private void GivenTheContentTypeIs(string contentType)
+        {
+            _inputRequest.ContentType = contentType;
+        }
+
+        private void ThenTheMappedRequestHasContentTypeHeader(string expected)
+        {
+            _mappedRequest.Data.Content.Headers.ContentType.MediaType.ShouldBe(expected);
+        }
+
+        private void ThenTheMappedRequestHasContentSize(long expected)
+        {
+            _mappedRequest.Data.Content.Headers.ContentLength.ShouldBe(expected);
+        }
+
         [Fact]
         public void Should_handle_no_content()
         {