Sharing a Custom Membership Provider

Sharing a Custom Membership Provider

I have an existing ASP.Net MVC 4 web application that has its own custom
(but very basic) membership provider with roles. I have created a new web
application (also MVC 4), and now I need to use the original custom
membership provider so that users of the first application can use the
same credentials to logon to the new application.
Both applications are using EF code first, and the first application has
the User/Roles modeled as User entities get recorded with actions such as
updates and object creation.
Maybe I need to decouple this part of the database, and use the repository
pattern to link different database contexts? I am getting out of my depth
here, and going in circles trying to figure out the best approach so any
direction appreciated.
Worst case is creating another membership provider (or using the ASP.Net
one) but I definitely want to avoid this if I can.