[NSBundle bundleForClass:[self class]] is dangerous because the code will behave differently depending on how AFNetworking is integrated.
If it is integrated as a static library (for example using CocoaPods), certificates will be searched in the main bundle.
If it is integrated as a framework (for example using Carthage), certificates will be searched in the AFNetworking framework.
Even though this behavior is documented, this is dangerous. Using the main bundle makes the behavior deterministic.