Provide endpoint discovery via closure for v3.
diff --git a/provider_client.go b/provider_client.go
index 7f8b892..3b9aaed 100644
--- a/provider_client.go
+++ b/provider_client.go
@@ -16,6 +16,9 @@
 
 	// TokenID is the most recently valid token issued.
 	TokenID string
+
+	// EndpointLocator describes how this provider discovers the endpoints for its constituent services.
+	EndpointLocator EndpointLocator
 }
 
 // AuthenticatedHeaders returns a map of HTTP headers that are common for all authenticated service requests.