Added security validation for User class

lib/User.js

@@ -295,6 +295,19 @@ class User {
 			}
 		}
 	}
+
+	async hasAccess(u) {
+		let [ userClasses, thisClasses ] = await Promise.all([
+			u.getClasses(),
+			this.getClasses()
+		]);
+
+		userClasses = userClasses.map(c => c.id);
+
+		return thisClasses.filter(c =>
+			userClasses.includes(c.id)
+		).length > 0;
+	}
 }
 
 module.exports = User;