Fixed parsing of incoming comma-separated list of Accept headers (#973)

Author: Bart Koelman

src/JsonApiDotNetCore/Middleware/JsonApiMiddleware.cs

@@ -16,7 +16,6 @@
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.Controllers;
 using Microsoft.AspNetCore.Routing;
-using Microsoft.Extensions.Primitives;
 using Newtonsoft.Json;
 
 namespace JsonApiDotNetCore.Middleware
@@ -120,7 +119,7 @@ private static async Task<bool> ValidateContentTypeHeaderAsync(string allowedCon
         private static async Task<bool> ValidateAcceptHeaderAsync(MediaTypeHeaderValue allowedMediaTypeValue, HttpContext httpContext,
             JsonSerializerSettings serializerSettings)
         {
-            StringValues acceptHeaders = httpContext.Request.Headers["Accept"];
+            string[] acceptHeaders = httpContext.Request.Headers.GetCommaSeparatedValues("Accept");
 
             if (!acceptHeaders.Any())
             {

test/TestBuildingBlocks/IntegrationTest.cs

@@ -63,16 +63,15 @@ public abstract class IntegrationTest
                 }
             }
 
-            using HttpClient client = CreateClient();
-
             if (acceptHeaders != null)
             {
                 foreach (MediaTypeWithQualityHeaderValue acceptHeader in acceptHeaders)
                 {
-                    client.DefaultRequestHeaders.Accept.Add(acceptHeader);
+                    request.Headers.Accept.Add(acceptHeader);
                 }
             }
 
+            using HttpClient client = CreateClient();
             HttpResponseMessage responseMessage = await client.SendAsync(request);
 
             string responseText = await responseMessage.Content.ReadAsStringAsync();