Synchronization between providers with different identifiers using Sync Framework

Question

I am trying to use Sync Framework to synchronize user data between Active Directory and an application providing a web service. I created two FullEnumerationSimpleSyncProvider classes, one for Active Directory and one for a web service, and created common columns of data types and metadata that can be shared by both. They are currently both capable of supporting their own ReplicaId and Metadata repositories.

The problem I am facing is that I do not know how to match the result from one provider to another, because they do not have the corresponding identifier information in their separate data stores and most of all the fields that could be used for matching one record with another are potential candidates for synchronization and cannot rely on 100% to provide an identity (for example, username, email address, etc.).

Is there a mechanism in Sync Framework that I can use to do some fuzzy matching to tell the structure how to match strings from one provider to another, since I don’t have a specific IdentityRule that I can create to match both ? Is something missing?

Thanks Mark