fix: CORS on assets api (#3659)

internal/api/http/header.go

@@ -40,9 +40,9 @@ const (
 
 type key int
 
-var (
-	httpHeaders key
-	remoteAddr  key
+const (
+	httpHeaders key = iota
+	remoteAddr
 )
 
 func CopyHeadersToContext(h http.Handler) http.Handler {
@@ -59,6 +59,14 @@ func HeadersFromCtx(ctx context.Context) (http.Header, bool) {
 	return headers, ok
 }
 
+func OriginFromCtx(ctx context.Context) string {
+	headers, ok := ctx.Value(httpHeaders).(http.Header)
+	if !ok {
+		return ""
+	}
+	return headers.Get(Origin)
+}
+
 func RemoteIPFromCtx(ctx context.Context) string {
 	ctxHeaders, ok := HeadersFromCtx(ctx)
 	if !ok {