Correct table structure for subdomains?

Question

Database design

Good evening. I'll go straight to the point.
There is a project that involves the creation of subdomains by users. Guests are registered as users, after which the user can create a 3rd level subdomain, http:// test .site.ru. Subdomains should be able to create categories and articles on that subdomain. How to properly design the structure of articles, categories, so that there is a link to a subdomain, that is, on the TEST subdomain ... only categories and articles belonging to this subdomain are shown. I threw in an approximate structure, but I can’t figure out where exactly to bind to a subdomain, either in categories, or in the articles themselves ... Tell me, how would it be more correct?
Category table

spoiler

Schema::create('categories', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('parent_id')->unsigned()->nullable()->default(null);
            $table->foreign('parent_id')->references('id')->on('categories')->onUpdate('cascade')->onDelete('set null');
            $table->integer('sort')->default(0);
            $table->string('name');
            $table->string('slug')->unique();
            $table->integer('visibility')->default(1);
            /*$table->integer('domain_id');
            $table->foreign('domain_id')->references('id')->on('domains')->onDelete('cascade');
            $table->unsignedInteger('domain_id')->index('domains_category_id_index');*/
            $table->string('type');
            $table->string('meta_description');
            $table->string('meta_keywords');
            $table->timestamps();
        });

Table of articles

spoiler

Schema::create('articles', function (Blueprint $table) {
            $table->increments('id');
            $table->unsignedInteger('category_id')->index('articles_category_id_index');
            $table->unsignedInteger('user_id')->index('articles_user_id_index');

            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
            $table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');

            $table->string('title');

            $table->string('slug')->unique()->index('articles_slug_index');
            $table->longText('content_source');
            $table->longText('content_rendered');
            $table->tinyInteger('visibility')->default(1);

            $table->text('meta_description');
            $table->text('meta_keywords');

            $table->timestamp('published_at');
            $table->timestamps();
        });

Answer 1

When creating another subdomain by a user, add the subdomain to the Subdomains(id, name, user_id) table, and simply add a unique subdomain_id field to the Articles table, and then each article will be strictly linked to a specific subdomain.
Alternatively, you can leave out the subdomain_id field in the Articles table and determine whether the subdomain belongs to the user who added the article. Do this using the Subdomains table, which I wrote about above. But it's easier to immediately add the subdomain_id field