AFN设置HTTP请求头

 AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
    manager.securityPolicy = [AFSecurityPolicy policyWithPinningMode:AFSSLPinningModeNone];
    manager.responseSerializer = [AFJSONResponseSerializer serializer];
    manager.requestSerializer = [AFJSONRequestSerializer serializer];
    [manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Accept"];
    [manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];