Sec-WebSocket-Extensions is a connection-level header.

We don't support any extensions currently, but it's important that when acting as a proxy, we don't pass through this header, since it could result in the client and server negotiating extensions that the proxy doesn't understand and will botch.

c++/src/kj/compat/http.h

@@ -89,7 +89,8 @@ namespace kj {
   MACRO(upgrade, "Upgrade") \
   MACRO(websocketKey, "Sec-WebSocket-Key") \
   MACRO(websocketVersion, "Sec-WebSocket-Version") \
-  MACRO(websocketAccept, "Sec-WebSocket-Accept")
+  MACRO(websocketAccept, "Sec-WebSocket-Accept") \
+  MACRO(websocketExtensions, "Sec-WebSocket-Extensions")
 
 enum class HttpMethod {
   // Enum of known HTTP methods.