代理post请求，返回405错误

## 背景
使用lightproxy代理的时候，get请求没问题，post请求会返回405 Method Not Allowed错误

## 问题排查
发现response header中返回了allow: GET

请问问题产生的原因以及解法。


Reproduce the report in LightProxy using the described GET and POST requests, then inspect the response headers for the 405 status and Allow: GET value. Trace where proxy handling distinguishes the two methods; done means identifying the cause and documenting or correcting the POST behavior, with a reproducible verification.

Written by the indexing model from the issue text.