c# HttpWebRequest not sending default credentials to proxy server

问题

I am using squid proxy server to authenticate the client before passing on the request to public network. I haven't set HttpWebRequest.Proxy object so I am assuming that the web request will take the default window credentials and pass on to the proxy server.

I have added an entry of the user to squid proxy as well, but I am getting the following error while making the request.:

(407) Proxy Authentication Required.

In squid logs, I am getting this:

TCP_DENIED/407 3722 CONNECT 

I have inserted the following block in App.config

<system.net>
    <defaultProxy useDefaultCredentials="true">
        <proxy
        usesystemdefault="true"/>
    </defaultProxy>
</system.net> 

To verify if there is discrepancy between the user credentials registered with squid and my windows user credentials. I tried opening a public website through browser which prompted for credentials as the request was passing through proxy server ( which I have set under Internet Options ), after entering windows credentials I was able to access that site.

Also, i checked through Fiddler ( a tool to check network traffic ) that the request to that proxy server didn't have Proxy-Authorization Header.

Can anybody please check and tell if something I have missed or I have made any mistake.

来源：https://stackoverflow.com/questions/38734738/c-sharp-httpwebrequest-not-sending-default-credentials-to-proxy-server