Add a stub to register role resolvers

lib/models/role.js

@@ -137,6 +137,17 @@ Role.RELATED = "$related"; // any User with a relationship to the object
 Role.AUTHENTICATED = "$authenticated"; // authenticated user
 Role.EVERYONE = "$everyone"; // everyone
 
+/**
+ * Add custom handler for roles
+ * @param role
+ * @param resolver The resolver function decides if a principal is in the role dynamically
+ *
+ * isInRole(role, context, callback)
+ */
+Role.registerResolver = function(role, resolver) {
+  Role.resolvers[role] = resolver;
+};
+
 /**
  * Check if a given principal is in the role
  *