feature: Implement <meta> tag fetcher from backends with allow-listed entries to prevent unwanted keys to pass

lib/challenge/refresh/refresh.go

@@ -47,8 +47,11 @@ func FillRegistration(state challenge.StateInterface, reg *challenge.Registratio
 
 		if params.Mode == "meta" {
 			state.ChallengePage(w, r, state.Settings().ChallengeResponseCode, reg, map[string]any{
-				"Meta": map[string]string{
-					"refresh": "0; url=" + uri.String(),
+				"Meta": []map[string]string{
+					{
+						"http-equiv": "refresh",
+						"content":    "0; url=" + uri.String(),
+					},
 				},
 			})
 		} else {