A general provider of a core registration service provides registration services to a special service provider. In one implementation, a first party presents a user registration form to a second party on behalf of a third party The first party receives registration provisioning data from the third party, which is used by the first party to generate a custom registration form. Responsive to receiving a request from a second party to register for a specialized service provided by a third party, the first party communicates the custom registration form to second party.