WordPress plugin to verify domain ownership — 2

I need a plugin to be used with my theme that fetches the value (domain name) from the user submitted custom post type and verifies the ownership of the domain.

I have a wordpress website where a user registers and enters his name, email, details etc. with the domain/website name in a separate input field. I want to authenticate/verify if that person is the real owner of the domain or not. Need a plugin for this.

When you quote please mention clearly how would you check the ownership.