关于afnetworking加入header

AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
    manager.requestSerializer = [AFHTTPRequestSerializer serializer];
    manager.responseSerializer = [AFJSONResponseSerializer serializer];
    //加入header的key和value
    [manager.requestSerializer setValue:value forHTTPHeaderField:key];
    NSLog(@"header-------%@",manager.requestSerializer.HTTPRequestHeaders);
    manager.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"text/html", @"application/json",@"text/plain", nil];
    [manager GET:urlStr parameters:nil progress:nil
         success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
             NSLog(@"-----------%@",responseObject);
         } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
             NSLog(@"error-------%@",error);

         }];