Website login plugin

Hi,

I’ve searched for a plugin, but I haven’t found it yet.
I’m looking for website login plugin.

When de visitor enters the website (landing page) they can choose between two options: a. visitor page and b. member page.
When they choose for b. member page, they have to fill in only a specific number to enter the following page/site. So no member plugin with a username and password needed, just entering a specific number.
If they enter the correct number, they are visiting the “hidden” site. If not they will be forwarded to the visitors site for normal access.

Which plugin can I use for this situation?

Thanks!
Laurens

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