We generally recommend that you define your verifiers in code and have them loaded by creating a class that implements the IVerifierProvider interface (which has one method called GetVerifiers).
If you still want to load them from xml, you can put them in the app.config/web.config and DiscoverVerifiersFromConfig() will load them from there. There also used to be a signature to load verifiers from a stream, which could have been sourced from xml in an database. If you guys still really want these features, we can bring it back, but we found that almost nobody was using it.