I want to create a website for a law firm, and they want a feature where they can provide every clients with a special number for his law suit and when the client signs in by the number along with his ID number to the website, he gets private access to all updates and important dates specifically for his law suit that the we provide for him my question is: is this feature already available? if not, how can I add it?
Something like this that you can modify to suit your own needs.
https://support.wix.com/en/article/corvid-tutorial-building-your-own-members-area
Or if they are already logged in, then you can just search by user id.
https://www.wix.com/corvid/reference/wix-users.User.html#id