Only use supported sort order for "explore/users" page (#29430)

Thanks to inferenceus : some sort orders on the "explore/users" page
could list users by their lastlogintime/updatetime.

It leaks user's activity unintentionally. This PR makes that page only
use "supported" sort orders.

Removing the "sort orders" could also be a good solution, while IMO at
the moment keeping the "create time" and "name" orders is also fine, in
case some users would like to find a target user in the search result,
the "sort order" might help.

![image](https://github.com/go-gitea/gitea/assets/2114189/ce5c39c1-1e86-484a-80c3-33cac6419af8)

routers/web/explore/user.go

@@ -10,6 +10,7 @@ import (
 	"code.gitea.io/gitea/models/db"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/sitemap"
@@ -79,10 +80,16 @@ func RenderUserSearch(ctx *context.Context, opts *user_model.SearchUserOptions,
 		fallthrough
 	default:
 		// in case the sortType is not valid, we set it to recentupdate
+		sortOrder = "recentupdate"
 		ctx.Data["SortType"] = "recentupdate"
 		orderBy = "`user`.updated_unix DESC"
 	}
 
+	if opts.SupportedSortOrders != nil && !opts.SupportedSortOrders.Contains(sortOrder) {
+		ctx.NotFound("unsupported sort order", nil)
+		return
+	}
+
 	opts.Keyword = ctx.FormTrim("q")
 	opts.OrderBy = orderBy
 	if len(opts.Keyword) == 0 || isKeywordValid(opts.Keyword) {
@@ -132,8 +139,16 @@ func Users(ctx *context.Context) {
 	ctx.Data["PageIsExploreUsers"] = true
 	ctx.Data["IsRepoIndexerEnabled"] = setting.Indexer.RepoIndexerEnabled
 
-	if ctx.FormString("sort") == "" {
-		ctx.SetFormString("sort", setting.UI.ExploreDefaultSort)
+	supportedSortOrders := container.SetOf(
+		"newest",
+		"oldest",
+		"alphabetically",
+		"reversealphabetically",
+	)
+	sortOrder := ctx.FormString("sort")
+	if sortOrder == "" {
+		sortOrder = "newest"
+		ctx.SetFormString("sort", sortOrder)
 	}
 
 	RenderUserSearch(ctx, &user_model.SearchUserOptions{
@@ -142,5 +157,7 @@ func Users(ctx *context.Context) {
 		ListOptions: db.ListOptions{PageSize: setting.UI.ExplorePagingNum},
 		IsActive:    util.OptionalBoolTrue,
 		Visible:     []structs.VisibleType{structs.VisibleTypePublic, structs.VisibleTypeLimited, structs.VisibleTypePrivate},
+
+		SupportedSortOrders: supportedSortOrders,
 	}, tplExploreUsers)
 }