直接在Access-Control-Allow-Headers后参照以下代码中加粗字体格式，添加自定义需要支持的header，以逗号隔开即可。

add_header Access-Control-Allow-Headers 'Accept, Authorization,DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';  

第1种。参考官方文档：

“When buffering is enabled, nginx receives a response from the proxied server as soon as possible, saving it into the buffers set by the proxy_buffer_size and proxy_buffers directives. If the whole response does not fit into memory, a part of it can be saved to a temporary file on the disk. Writing to temporary files is controlled by the proxy_max_temp_file_size and proxy_temp_file_write_size directives.

When buffering is disabled, the response is passed to a client synchronously, immediately as it is received. nginx will not try to read the whole response from the proxied server. The maximum size of the data that nginx can receive from the server at a time is set by the proxy_buffer_size directive.”

可以试着打开debug日志，然后看日志中记录哪里处理时间较长

配置方法：error_log  /tmp/debug.log debug;