Keep baggage, tracestate, and traceparent with previous casing

Author: benaadams

src/Http/Headers/src/HeaderNames.cs

@@ -65,7 +65,7 @@ public static class HeaderNames
         public static readonly string Authorization = "Authorization";
 
         /// <summary>Gets the <c>baggage</c> HTTP header name.</summary>
-        public static readonly string Baggage = "Baggage";
+        public static readonly string Baggage = "baggage";
 
         /// <summary>Gets the <c>Cache-Control</c> HTTP header name.</summary>
         public static readonly string CacheControl = "Cache-Control";
@@ -248,10 +248,10 @@ public static class HeaderNames
         public static readonly string Translate = "Translate";
 
         /// <summary>Gets the <c>traceparent</c> HTTP header name.</summary>
-        public static readonly string TraceParent = "TraceParent";
+        public static readonly string TraceParent = "traceparent";
 
         /// <summary>Gets the <c>tracestate</c> HTTP header name.</summary>
-        public static readonly string TraceState = "TraceState";
+        public static readonly string TraceState = "tracestate";
 
         /// <summary>Gets the <c>Upgrade</c> HTTP header name.</summary>
         public static readonly string Upgrade = "Upgrade";

src/Servers/Kestrel/shared/KnownHeaders.cs

@@ -387,6 +387,14 @@ public class KnownHeader
 
             private string ResolveIdentifier(string name)
             {
+                // Check the 3 lowercase headers
+                switch (name)
+                {
+                    case "baggage": return "Baggage";
+                    case "traceparent": return "TraceParent";
+                    case "tracestate": return "TraceState";
+                }
+
                 var identifier = name.Replace("-", "");
 
                 // Pseudo headers start with a colon. A colon isn't valid in C# names so