Switching to Windows Identity Foundation - Should we use the SQL Server role and membership provider?

Question

We have an application which uses SQL Server as the back end. It was client server based, now it will be web based. Our implementation to logon was a user ID and password hash/salt stored in the database. Additionally, all policies and roles were stored in our table schema and assigned to users and or user defined groups. So, they would login, authenticate, and then we would pull the role(s) and policies for that user so they could use the parts of the application that thier role(s) and policies allowed for.

We are investigating WIF now that it is web based.

Ideally we would like to re-use our current model, that is, be able to logon using our existing table(s) and then pull the roles and polices afterward.

However, there is a SQL Server role and membership provider.

Would it be easier to switch the login, roles, and membership using the built in SQL Server provider and deprecate our table schema? Or should we build a provider from scratch?