Restricted access page login

Good day folks.

Please help. I’ve been trying to figure this out for days…

I have imported contacts (and their email addresses) that I have invited to an event into WP Users.

I have tried a number of RSVP plugins, but none of them are exactly what I want.

Is there a way to restrict access to the RSVP page, but allow these contacts to login by just using their name and/or email address without their having to register first? I don’t want just anyone to be able to RSVP, only those invited and I don’t want invited guests to have to go through the trouble of registering just to RSVP.

Thanks in advance,
Sam