Added Const for use of CtxKeys (#1511)

* Added Const for CtxKeys

* Move CtxKey Const declarations

* Fixed tests

* fix test

caddyhttp/httpserver/middleware.go

@@ -197,3 +197,16 @@ var EmptyNext = HandlerFunc(func(w http.ResponseWriter, r *http.Request) (int, e
 func SameNext(next1, next2 Handler) bool {
 	return fmt.Sprintf("%v", next1) == fmt.Sprintf("%v", next2)
 }
+
+// Context key constants
+const (
+	// URIxRewriteCtxKey is a context key used to store original unrewritten
+	// URI in context.WithValue
+	URIxRewriteCtxKey caddy.CtxKey = "caddy_rewrite_original_uri"
+
+	// RemoteUserCtxKey is a context key used to store remote user for request
+	RemoteUserCtxKey caddy.CtxKey = "remote_user"
+
+	// MitmCtxKey stores Mitm result
+	MitmCtxKey caddy.CtxKey = "mitm"
+)