Added Class.hasAccess to validate user input and add security

lib/Class.js

@@ -196,6 +196,14 @@ class Class {
 		return await Promise.all(testObjects);
 	}
 
+	async hasAccess(u) {
+		const userClasses = await u.getClasses();
+
+		return userClasses.filter(c => {
+			return c.id === this.id;
+		}).length;
+	}
+
 	addTeacher() {
 
 	}