Looking for Facebook API Ninja for Consultation

We are creating a page builder for our current customers and this page builder allow them to create a webform to collect new leads. Our users can use our own domain to publish their webpages or publish to their own server. We would like to add to this form the ability for people to signup using Facebook. When we create a facebook application, we have to provide a site URL. When user will publish the website to his own server, we cannot use our own facebook application id because the domain is different. We want to use ONE SINGLE Facebook application ID of our own for every website no matter what the domain is. We are looking for someone to point us to a new solution or have an idea how we can achieve that. You don't need to code anything, we are just looking for someone that has done this in the past or knows the solution to this problem and tell us what it is. We want you to discuss this with us via a Skype call where we can share the screens of our application with you and you can tell us what could be the solution. Thanks in advance.