Hi @dvoinikat
Pre: In Power Apps Portal management:
1. Create web roles (Ex: TableUsers)
2. Create a new web page and add an entity list and link your table which you have created.
3. Create table permissions for your custom table
From the Power Apps Portal point of view, the easiest way is to request the user to sign in via Azure AD into the portal. Once contact is created assign a web role that will allow the added users to access only the table which you have created.
If you are not after any of the above, then you can simply add the user as the "Basic user" of your environment. This will allow your users can see your tables.
Hope it helps.
------------
If you like this post, give it a Thumbs up. Where it solved your request, Mark it as a Solution to enable other users to find it.