C# Connecting Through Proxy

This is easily achieved either programmatically, in your code, or declaratively in either the web.config or the app.config.

You can programmatically create a proxy like so:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("[ultimate destination of your request]");
WebProxy myproxy = new WebProxy("[your proxy address]", [your proxy port number]);
myproxy.BypassProxyOnLocal = false;
request.Proxy = myproxy;
request.Method = "GET";
HttpWebResponse response = (HttpWebResponse) request.GetResponse();

You're basically assigning the WebProxy object to the request object's proxy property. This request will then use the proxy you define.

To achieve the same thing declaratively, you can do the following:

<system.net>
  <defaultProxy>
    <proxy
      proxyaddress="http://[your proxy address and port number]"
      bypassonlocal="false"
    />
  </defaultProxy>
</system.net>

within your web.config or app.config. This sets a default proxy that all http requests will use. Depending upon exactly what you need to achieve, you may or may not require some of the additional attributes of the defaultProxy / proxy element, so please refer to the documentation for those.

If you are using WebClient, it has a Proxy property you can use.

As other have mentioned, there are several ways to automate proxy setting detection/usage

Web.Config:

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

Use of the WebProxy class as described in this article.

You can also cofigure the proxy settings directly (config or code) and your app will then use those.

Web.Config:

<system.net>
  <defaultProxy>
    <proxy
      proxyaddress="http://[proxy address]:[proxy port]"
      bypassonlocal="false"
    />
  </defaultProxy>
</system.net>

Code:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("url");
WebProxy myproxy = new WebProxy("[proxy address]:[proxy port]", false);
request.Proxy = myproxy;
request.Method = "GET";
HttpWebResponse response = (HttpWebResponse) request.GetResponse();

If you want the app to use the system default proxy, add this to your Application.exe.config (where application.exe is the name of your application):

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

More details can be found on in the MSDN article on System.Net

Try this code. Call it before making any http requests. The code will use the proxy from your Internet Explorer Settings - one thing though, I use proxy.Credentials = .... because my proxy server is an NTLM authenticated Internet Acceleration Server. Give it a whizz.

static void setProxy()
{
    WebProxy proxy = (WebProxy)WebProxy.GetDefaultProxy();
    if(proxy.Address != null)
    {
        proxy.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
        WebRequest.DefaultWebProxy = new System.Net.WebProxy(proxy.Address, proxy.BypassProxyOnLocal, proxy.BypassList, proxy.Credentials);
    }
}

This one-liner works for me:

WebRequest.DefaultWebProxy.Credentials = CredentialCache.DefaultNetworkCredentials;

CredentialCache.DefaultNetWorkCredentials is the proxy settings set in Internet Explorer.

WebRequest.DefaultWebProxy.Credentials is used for all internet connectivity in the application.

Foole's code worked perfectly for me, but in .NET 4.0, don't forget to check if Proxy is NULL, which means no proxy configured (outside corporate environment)

So here's the code that solved my problem with our corporate proxy

WebClient web = new WebClient();
if (web.Proxy != null)
    web.Proxy.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;

This code has worked for me:

WebClient wc = new WebClient();
wc.Proxy.Credentials = CredentialCache.DefaultCredentials;

Automatic proxy detection is a process by which a Web proxy server is identified by the system and used to send requests on behalf of the client. This feature is also known as Web Proxy Auto-Discovery (WPAD). When automatic proxy detection is enabled, the system attempts to locate a proxy configuration script that is responsible for returning the set of proxies that can be used for the request.

http://msdn.microsoft.com/en-us/library/fze2ytx2.aspx

            var getHtmlWeb = new HtmlWeb() { AutoDetectEncoding = false, OverrideEncoding = Encoding.GetEncoding("iso-8859-2") };

            WebProxy myproxy = new WebProxy("127.0.0.1:8888", false);
            NetworkCredential cred = (NetworkCredential)CredentialCache.DefaultCredentials;
            var document = getHtmlWeb.Load("URL", "GET", myproxy, cred);

I am going to use an example to add to the answers above.

I ran into proxy issues while trying to install packages via Web Platform Installer

That too uses a config file which is WebPlatformInstaller.exe.config

I tried the edits suggest in this IIS forum which is

<?xml version="1.0" encoding="utf-8" ?>
<configuration>  
  <system.net>    
     <defaultProxy enabled="True" useDefaultCredentials="True"/>      
   </system.net>
</configuration>

and

<?xml version="1.0" encoding="utf-8" ?>
<configuration>  
   <system.net>    
     <defaultProxy>      
          <proxy 
               proxyaddress="http://yourproxy.company.com:80" 
               usesystemdefault="True"
               autoDetect="False" />    
     </defaultProxy>  
   </system.net>
</configuration>

None of these worked.

What worked for me was this -

<system.net>    
    <defaultProxy enabled="true" useDefaultCredentials="false">
      <module type="WebPI.Net.AuthenticatedProxy, WebPI.Net, Version=1.0.0.0, Culture=neutral, PublicKeyToken=79a8d77199cbf3bc" />
    </defaultProxy>  
 </system.net>

The module needed to be registered with Web Platform Installer in order to use it.