Good Pattern design?

I have to design and implement an eligibility service: -The user will login and we already have an implemented object IAuthenticationProvider which already implements: GetUserId().

To get if the user is eligibible for certain products, we need to connect with a legacy service which eventually will be replaced by a new one. It returns if user is eligible or not, and the the current subscription type that the user has.

Based on the type of the subscription that we have, we should call to other service to get the products which is can purchase.

I am not good designing, so basically is to connect to two different services, and consolidate the information, and apply some rules over this. Consider that subscription type service and product to purchase service can be new or legacy services, which will eventually will be changed.

Any ideas about patterns?

thanks!