AFNetworking 请求头的设置

1. AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];  
2. manager.securityPolicy = [AFSecurityPolicy policyWithPinningMode:AFSSLPinningModeNone];  
3. manager.requestSerializer = [AFJSONRequestSerializer serializer];  
4. manager.responseSerializer = [AFJSONResponseSerializer serializer];  
5. [manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Accept"];  
6. [manager.requestSerializer setValue:@"application/json; charset=utf-8" forHTTPHeaderField:@"Content-Type"];