AFNetworking 2.0 and HTTP Basic Authentication

AFNetworking 2.0 new architecture use serializers for creating requests and parsing responses.
In order to set the authorization header, you should first initialize a request operation manager that replaces the AFHTTPClient, create a serializer and then call the dedicated method to set the header.

For example you code would become:

AFHTTPRequestOperationManager *manager = [[AFHTTPRequestOperationManager alloc] initWithBaseURL:[NSURL URLWithString:@"http://examplewebsite.com"]];
manager.requestSerializer = [AFHTTPRequestSerializer serializer];
[manager.requestSerializer setAuthorizationHeaderFieldWithUsername:@"userName" password:@"password"];

You should read the documentation and the migration guide to understand the new concepts that come with the version 2.0 of AFNetworking.